I can hear the tl;dr coming already. 
Here it comes, baby...I can't make art. I've tried, I find myself not being able to make my games because of my lack of art! I don't want to use public domain assets because someone else might be using them and it might look like I'm copying them. I've tried 2D, 3D (waay to hard), I can't do it! Please help
Use science!
I was in exactly the same boat as you 4-5 years ago. Zero talent at art - had poked at it, and obviously didn't have "the gift." I was in the middle of college, and was getting really worried because I couldn't get anyone to make art for my games. With my back against the wall, I decided to try anyways, figuring I'd at least learn how to work with artists even if I couldn't become one.
For the first year or so, I approached art with no methodology at all. I just tried doing stuff by "feel", and it pretty much all sucked. After that, I stepped back, and said "okay, hold on - I'm an engineer. Let's try thinking about this problem
like an engineer." Let's form hypotheses about what I'm doing wrong. Let's lock variables. Let's test ideas with heavy iteration. It worked.
Most of art is science. Shading .. is merely running a human-optimized raytracing algorithm in your brain. We're poor at casting individual rays, but we're amazing at interpolation. Anatomy is fairly cut and dry - it tells you how the human body can - or cannot, bend and twist. Bend it the right way, your drawing looks graceful. Bend it the wrong way? Your drawing looks uncomfortable. Optics tells us how the eye sees different colors, and how colors are related to each other. Optics tells us you can do stuff like putting grey next to blue, and the grey will look yellowish.
Anyways, besides all the theory, the scientific method can really help as you practice. The biggest danger with practice is that
practice alone won't make you good. That's really scary. I've seen people churn out dozens of drawings every week; a huge volume more work than I do, and they've been doing it for years without getting any better. I'd link some particular webcomic artists, but to avoid being a dick, I'll just say that some members of the top-50 comics out there are perennially terrible*, and have put out thousands of pages. So what gives?
The key to having practice actually make you good, is that
you must change how you do things, and test if that change makes your work better. You can't just repeat the exact same recipe-for-failure you've always been using, and expect the results to come out differently - they won't. Same input, same output. Practice simply gives you the time to make these tests.
Studies are a key way to do this. The trick with studies, is that they're optimized to get the highest concentration of "tests", in the least amount of time. If you're practicing positioning the nose on a face - the easiest optimization, is just to forget about drawing the body at all. You'll see artists do this all the time - whole pages of nothing but faces, over and over. Or hands, or legs, or whatever the focus is. Likewise, they'll be very sketchy - if the sketch is enough to see if it's right or wrong, why waste 10x as much time "cleaning up" each individual drawing of a leg, when you could do 10x as many trials? 10x as many trials, is 10x as much learning! A key trick in doing studies is to
stop after you've crossed the point of diminishing returns for "learning value", and get on to another study.
Another idea I mentioned is locking variables. When testing hypotheses, it's really hard to know if they're really the deciding factor, if everything else is changing too. Like, if you're trying to get the hang of drawing features on faces, it can be nigh-impossible to tell if you're getting it right, if every time you draw the face, the face itself is pointing in a different direction. So do dozens of tries with the same face. Digital tools are a great way to do this, because not only can you cut and paste, but "trying something, then pressing undo, and then trying it again" is itself a huge form of iteration. If, every single time you try to do that, you're drawing a nose onto a face, pretty soon, you'll get the hang of putting it in the right place.
A piece of advice I would give to the OP is to just ape the shit out of artists that you like. Maybe this is a controversial statement, but it's a really quick way to learn.
But when I say 'ape', I don't mean the outright tracing/plagiarism you find so readily on sites like Deviantart. To clarify, you should see what kind of techniques a given artist uses and take from them what you will.
It's controversial only to some modern people with delusions of ownership being a 'natural right'. It's perfectly legal under fair use (as long as you don't claim the work as yours), and it's a time-honored tradition of art known as "Studying from the Masters". In renaissance times, people would do exactly that - they'd actually sit down, as a group, and meticulously practice drawing parts of the master's work - such as directly imitating something from da vinci. Da vinci himself did it, and recommended the practice. It was and still is (at least at some schools) a key part of curriculum. You should always attempt making your own solutions to these "engineering problems", but it's also very good to study how other people solved the same problem. Sometimes it's just not possible to come up with a new, innovative way to it; so use what works.
In fact, back in the day, this used to actually be legal trade. Quite a few people made a white-market (e.g. not illegal, but encouraged) living making duplicates of masterpieces; especially since at the time, there was no photography, and no other means to mass-produce a work if you wanted one for your home (understandably, due to the labor involved, it was expensive enough that only rich people could buy them), but it's interesting that these were not viewed as deceptive "forgeries". They were openly copied, and everyone was fine with the practice. If you've ever read Nathaniel Hawthorne's
The Marble Faun, he describes this practice in great detail, and it's a central story element that one of the leading characters was particularly skilled as a copyist; able to infuse her work with a "fire and soul" that some people felt exceeded the originals (IIRC).
But the point is that studying from the masters is a great way to "lock variables", and piggyback on something they kick ass at, but which you're terrible at. You can imitate aspects of their work, in order to practice some other skill of yours - perhaps, you can trace over some professional's anatomy ... in order to practice putting clothes on figures? This can't be sold or distributed as your own work, but it's perfectly fair game for
practice. Much more common, is inking and coloring someone else's line art, to practice your coloring and shading.
Also, as John said, you can side-by-side, attempt to recreate the aspects of their work, which you found impressive, and by walking in their shoes, you're walking through solving the same problems they did. If you just "trace" their work, you won't learn anything, but if you force yourself to solve the same problems they did, using your own knowledge and skills, the master's work is an excellent way to tell if your methods are working or not. For example, maybe you're drawing an arm in a similar pose. You look back at the master-work, and realize there's a certain curve to part of their arm that just isn't in your repertoire. Clearly, they (probably**) know something you don't, and you've stumbled on something new to learn! So then you bust open your anatomy book and discover a whole new muscle (or gap between) there (for a simple example, the gap between the triceps and deltoid).
Counterpoint: So I gave all this long jive about being systematic to improve your skill. Be willing to compromise everything I just suggested, for one key factor:
keep art fun. If it stops being fun, you stop practicing. No practice, no skill gain. Dead stop. Keeping stuff fun, at all, can actually be incredibly hard. Balancing fun with also frequently doing it is harder still - you won't get very far if the only time you practice drawing is just once or twice a month, on those rare occasions when you "actually feel like it".
I have a bad feeling that the unlucky "rest of us" who don't naturally enjoy drawing 24/7 basically have to "brain-hack" ourselves into making it fun when it wouldn't naturally be. I still have a great deal of difficulty with this, and no bulletproof answers - I find myself cursing my ennui and laziness all the time.
* This speaks to an important point. Art quality matters, but this stuff isn't just one dimension of quality. People can like a work even if it's art is terrible - or much more commonly, with comics, it is different dimensions in just the art, that can outweigh each other. Comic artists sometimes have bad anatomy, but are liked because their characters are funny and expressive and in that particular usage, that matters more. Not something to hang on your wall, but something that manages to make you laugh.
** obviously, they're not perfect, which is why you need to supplement any "study from the masters" with "studying from life". Spend too much time imitating other artists, rather than imitating real-life, and you run a danger of being like
Rob Liefeld
Developer
