You say you're looking for "techniques", but how much skill do you have at drawing in general?  If you haven't trained your perception or gained some understanding of the basic principles, any particular tricks for one program/medium or another aren't going to help much.

Making great art takes a lot of practice, it's true.  That said, I would have to disagree with the idea that practice is the *only* way to make your art better, particularly if you're a beginner.  There are certain things that you can learn that will improve your art immediately, and there's nothing wrong with using those as long as you realize that they won't immediately lead to perfect art.

Here's an art tutorial for programmers that's pretty good:

http://www.gamedev.net/page/resources/_/creative/visual-arts/better-prog...

As you can see, the ultimate result of the above tutorial isn't something amazing, but what it does give you is something a bit more usable than typical beginner art.

Here's some other stuff:

Color Theory

A lot of programmers who are just getting started with art tend to think of color in terms of red, green, and blue.  This is a horrible way to think of colors if you want your art to look natural.  If you haven't done this already, the absolute first thing you need to do is start picking your colors with HSV sliders as opposed to RGB ones.  RGB sliders tend to lead people to make unsubtle color decisions, such as using pure green for grass, etc (this is one of my personal pet peeves; it's so easy to choose a natural color for grass, even for a beginner, but som many people just pick #00ff00 and end up with really unnatural-looking grass).

To get a bit further into the color thing, you need to know a couple of basic things about light and shadow.  In a natural environment, light and shadow have their own colors.  If you're standing outside in broad daylight and look at your shadow, your brain tells you that the color of your shadow is just a darker version of the surrounding color.  This isn't actually the case.  In reality, on a sunny day, there are two major sources of light:  The sun, which is yellowish, and the sky, which is bluish.  Your shadow is still receiving light, or else it would be pure black.  That being said, the reason you have a shadow is because you're blocking the sun from hitting that area, so the main source of light to that area is going to be the sky.  As such, shadows tend to be more blue than the surrounding area.

This is of course different on an overcast day, or when you're inside (because the ambient light in the room is the color of the walls an ceiling), but as a general rule for beginners, make your highlights a bit more yellow and your shadows a bit more blue, and you'll end up with art that looks significantly better than someone who doesn't already know this.

Use Photo References

Short of actually tracing a photo (or pasting content from the photo into your art), it is always okay to use photos as references, even in finished art.  That being said, I would stop short of encouraging anyone to just paint or draw exactly what they see in a photo.  Look at a number of different photos and combine elements from them into what you want.  If you're drawing a person, it's fine to look around until you find a photo of a person with the correct pose and body type.

Note that since you can't get in legal trouble as long as you don't trace, it's also fine (and encouraged) to credit your reference photos.

If the photo is released under a Free license, it's also okay to trace the photo, but understand that in that case your work is a derivative work and you need to follow the terms of the license.

Everyone wants to be able to draw awesome stuff right from their imagination, but that is one thing the definitely takes tons and tons of practice (artists will often talk about having a 'mental library' that they can use).  You need to remember, though, that what's important is the quality of your ultimate result, not how you arrived at it.  DO NOT BE ASHAMED OF REFERENCING PHOTOGRAPHS.  PROFESSIONAL ARTISTS DO IT.

The Pen Tool

Tablets are great, don't get me wrong.  If you're going to be doing serious artwork over a long period of time, I would strongly advise you to get a tablet.  However, it's also important to note that a tablet is only as good as your drawing arm (practice, practice, practice).  If you're one of those people who has a bad arm but a good eye, then the Pen Tool is your friend.  Advanced drawing programs (Photoshop, GIMP, Krita, etc) can generally stroke a pen line as if you're using a brush.  Hence, if you have time, you can assemble something line by line making adjustments with the pen tool, and end up with a result that's nicer to look at than if you'd painted it directly.  If you use a vector drawing program (like Inkscape), you can continually make adjustments to your strokes as opposed to being stuck with them once you're done.  If you're not a fan of the vector style, you can always start in a vector program and then go to a raster program once you have everything drawn out.  Some raster programs also let you work with multiple pen strokes, so you can accomplish this without using a vector program in some cases.

Layers

Use them.  Seriously.  Have a white background layer, then paint on the layer above it.  Have shadow and highlight layers.  Don't paint on your rough sketch layer, particularly if your sketch layer is a scan of an image.  You don't want to have to clean up pencil lines in your final work.

Brushes

Use a mostly solid brush with a slightly soft edge, as opposed to using a brush that's completely soft.  Brushes that are soft all the way to the middle look terrible when you use them to fill an area, because the area gets filled incompletely.  Using a solid brush also helps you to think of your shading and highlights in terms of solid areas rather than lines.  You'll break this rule later, but it's good to follow it as a beginner.

Art Programs

Use whatever program that gives you the results you like the best.  Certain programs act in different ways.  Try a bunch of them before you make up your mind.

Practice :)

In the long run, if you want to be really satisfied with your art, practice is the only way to go.  That being said, practice has a lot more value if you understand what it is you're trying to get from it.  As an artist, you need to understand the visual tricks that your brain plays on you, and be able to see the world as it really is (the light and shadow thing from above is an example of this).  When you draw the world, think hard about what you're observing, and make special note of the things where there's a difference between what you think you see and what you actially see.

Here's an art tutorial for programmers that's pretty good:

http://www.gamedev.net/page/resources/_/creative/visual-arts/better-prog...

I disagree.  All of the points offered on that link have some amount of merit, but the way many of them are presented has the potential to be very misguiding.  Case in point, going for a quirky style in your graphics can be a great thing and certainly a well-done stylistic approach is preferable over a lackluster realistic one, but in drawing you should never say "I meant to do that" unless you well and truly did.  Style isn't about covering over your mistakes with an excuse of "that's just how I roll" but about consciously choosing to make things look a certain way.

(The advice in bart's post itself is all pretty good, though.)

Ya know, it's intresting.  This isn't really a politically correct thing for someone involved in art to say, but I have to say I'd agree to some extent with what Gwes said about style -- if you don't have the skill to choose your 'style' it's not really your 'style' per se, it's just the limit of your artistic ability.  If someone says "I think all art is good and everyone has their own style" then often times they're just making excuses for a lack of skill on someone's part. :)

That being said, though, realistically it's difficult sometimes to find someone to do art for your project, and you may want to produce a project that looks reasonably good without spending many hundreds or thousands of hours practicing art (I feel like I read somewhere that on average, to get truly good at something, you have to spend about 10,000 hours doing it).  If you understand that what you're doing is recognizing your own limitations and working within them, it's not so much about being in denial as taking an engineer's approach.  "Here are the resources I have at my disposal -- what can I do with them that will look good?"  In that case, the highly stylized approach isn't about trying to convince yourself that you're a good artist; it's about understanding that you're a beginner and working within your limits.  This will rarely (if ever) give you an end result that would be as good as if you're an experienced artist, but it can give you a much better result than if you don't take your limitations into account (and getting an experienced artist on your project isn't always in the cards for everyone).

The end result is what matters. Work with an undersatnding of your abilities and resources and produce the best results that you can.  Skill will come with practice.

I'm thinking I might add onto this and turn it into a real tutorial.

Ah, that's an interesting subject there.  To some extent, the resolution of the images is too low to tell exactly how it was done, so I can make two guesses:

One possibility is that they scenes are rendered in a 3D renderer and then retouched.  In my personal experience, though, building a realistic-looking natural scene in a 3D renderer requires even more time and skill than just painting one from scractch.  As such, I'm leaning toward saying that this isn't what they actually did.

The second (and more likely) possibility is that they did what's called "Matte Painting".  My understanding of matte painting is that you're essentially doing whatever you can to create an image that's as real as possible.  Matte painting doesn't, to my knowledge, involve a particular set of rules.  People will often mix photos along with 3D renders and digital painting to produce images that are at least somewhat convincingly realistic (as opposed to stylized in some way).

If you're going to be taking this route, you'll want to make sure you have a valid license to use any photographs you're taking pieces from (this reaches into the area of fair use, which is decided by the courts on an individual basis -- generally it's best to have a valid license and avoid fair use questions altogether).

Actually, I'd like to add this section as an amendment to my main post:

"Cheating"

When you set out to make art, it's important to think about why you're making that art.  If you're making creating it in order to learn, then you probably want to do things the hard way, and force yourself to grow.  If your purpose is to make a piece of art that looks as nice as possible with your existing skill set (say, for a game), then you should strongly consider "cheating".  I'm not talking about doing anything illegal here (such as plagiarism) -- what I'm referring to as "cheating" in just the act of using your tools and resources to your greatest advantage without regard to purism or doing things the "right" way.

There are a number of things you might do in order to cheat. 

For interiors, particularly futuristic ones, if you have some amount of skill building 3D environments, then grab a program like Blender and build your interior in there.  Render it with cycles (or some other engine that supports physical lighting), and then paint over the entire thing with digital paints so that the original render doesn't show through at all.  In doing so, you've just effectively "cheated" and allowed a computer to figure out your perspective and lighting for you (both of which can be difficult for a beginner to do realistically).

Also, there's nothing wrong with painting over a photograph (provided you have the license to do so, and give proper credit).  If you need a digital painting of an outside environment, search Flickr (or some other website where you can find CC-licensed photographs) and find an image that you like, then paint over it.  Remember, if you're making art for a game, you're concentrating on the end result, not the process.

One tip for paintovers and blending in general -- your paint program probably has a hotkey that you can hold down that changes the brush tool into the eyedropper tool.  If you're painting over a photo or trying to blend colors, learn to use the hotkey without jumping to your toolbox every time you want to switch.

More on "cheating"

Modern paint programs are good allowing you to distort things in very specific ways.  If you want to paint ground, for instance, you can paint a splotchy pattern in the general color scheme that you want, and then use your paint program's perspective transform to make the ground look flat.  If you watch videos of people speed-painting environments, you'll see this a lot.  Another thing you can do is if you draw something and aren't satisfied with the proportions, you can use the transform tools to tweak the proportions of whatever it was you drew (be it a person, an object, or whatever).  This is of course better done in the rough phase, so the inevitable ugliness left over from the transform won't be part of the final product. :)

Sorry to keep randomly posting this stuff.  I'm trying to build up enough content for a real tutorial. :)

@bart: you call that cheating? I call it getting the job done ;)

Using 3D application to help with the perspective, well thats a creative use of the tools you have.

Here are some tutorials on 2D game art using vectors (based on inkscape but nearly all other vector tools allow you to do the same things):

http://2dgameartforprogrammers.blogspot.com.au/

it's helpful to start with the earlier posts and work your way to the more recent one. Especially the last posts with the Apache helicopter can be a little intimidating. Enjoy!

If you want to learn it (and not just create the best you can with you current skill level) I would suggest to get a pencil, some paper and draw with that.

Start a "sketch book" and dont show it to anyone, to make sure you feel comfortable to draw ugly. You will draw alot of things that look bad (everyone does it), but you will learn threw that.

Draw by reference to learn something new. i.E. google for "face" and draw 10 noses, heads, whatever. (Dont publish them / possible licence violation).

If you also drawing with a tablet, get a second monitor.

Most importantly, keep your fun! Just making studies may be good for your drawing skills, but it becomes boring, so dont over do such things.

Something I'd add here is that everyone's brain works a different way. I'm not good at drawing, painting or 3D modeling, but during the LPC I found I actually enjoyed and was decent at pixel art. Try lots of different styles/methods and eventually you'll find one that really resonates with you.

While its true that not everyone is the same I just want to add that 2 years ago I couldn't draw a simple line and if I tried to draw something it looked like it was drawn by 3 year old.

Then I decided to learn to draw and bought a wacom tablet. Just some weeks later I improved so much that friends said to me "wow you are really talented, not like me...I wish I could draw like you". The answer was always the same: "I don't have any talent, just start to draw and you will improve."

'Pixel art' is different then '2d game art'. A lot of modern game art is made using vector graphics...

I will suggest you to first master the pen tool in any graphic program like Inkscape, Illustrator or Photoshop. Also try to replicate the graphics you like. Using references is the best way to learn. I am also learning game art. You will find these links useful.

http://unluckystudio.com/10-best-photoshop-tutorials-to-learn-game-art/

http://unluckystudio.com/creating2dgameart/

Hi. 

What I can tell you, first is what do you want to do? 3d? pixel? ilustrative/digital art?

You have to know well what you want and of course there will be be somethings there that will be innate to you. Use your strongpoints always.

For example I am very good at pixel I can design or form very well the human body when doing pixel and when drawing it by pencil I am mediocre, I dont know why.

Through the years I have learned that the most difficult area is drawing by hand, followed by sculpture, then painting and then pixel.

Now I use my strenghts as I cant draw very well comics so I put my efforts at 3d and pixel even if I know I would like to draw comics but I know I am better at those areas. Just observe and see what areas you are good and everything will be easier.

As for what to do, just copy or try to simulate your favorite styles or games, I do for example a lot of brawl characters because those are what I loved and I try to learn to animate them too. If you need references use them always to observe, have them in your HD but only study them, that way you will learn faster than only copying.

Cheers.