I'd probably add shading and lighting like that to my work, but I'm afraid I'd add too much, so I just stick to basic shadowing. Not that it's much of a problem, since I rarely draw nowadays, though I'd like to get back to it so I can get better. Any tutorials you'd recommend?
That's the beauty of digital art though! You can add it (maybe in a separate layer if you aren't sure) and then go back and delete it easily if you don't like it. I actually used to have the problem of not having enough contrast in my shading. My art teachers told me I had to stop being scared of putting darker tones when needed (well, they didn't say 'scared', but I think that's what they were getting at). I was feeling like my digital stuff was getting stale and this got me back in the groove again. I actually do all mine through trial and error, so don't really have any tutorials to recommend. I'm sure there are tons on here though.