Hey there! Just popping in after seeing this thread title pop I up in the "most recent" box, thought I'd give it a browse. It's really nice to see someone who seems intent on doing different approaches to their pictures! When I was frequenting dA too often I saw artists stick to the same methodology and they'd stagnate. I suspect you will not have this difficulty!
Anyway, if I could suggest some things that I think might springboard your stuff a bit further:
1) something I and a classmate of mine used to do a lot in school - since we weren't sure where we wanted our lines to be, we kinda... back-and-forth'd them a lot until the "shape" of what we wanted was gradually carved out. This is okay at first but it's very habit forming! Try to get into the habit of making
one or two decisive, longer lines for your lineart, even when sketching. (erase things that are really wrong.) It can be
super tough but once you get into the habit you don't have to relearn it. (I find a lot of art is like this... I used to struggle with perspective a lot, and while I don't have it down 100%, I don't remember crossing into a point where I was suddenly mostly okay with it. But I am now, so ?????)
2) I think this is kinda fun... when digital, get into the habit (another habit!! :O) of
putting down a base colour that isn't white before you start, and draw on top of it. Middle-colours work best to start with, even grey is better than white. Using black and white (or very strong/bright colours) can skew your colouring and make it too easy to have overly darkened/washed out/over exposed images! ((I can't talk re: saturation though. I'm pretty bad with oversaturation. Gotta use more neutral shades :( )) If you challenge yourself by painting with very opaque, high-transparency brushes, you can get some really neat shading by letting the background colour show through in the darker parts of your image :)
3) even more fun!! this is more of a crazy challenge than an actual suggestion, but I've seen lots of people do it and I have a blast doing it myself. After doing your sketch on your base colour, open up a new layer, and just
BLOB random colours all on top of the image. Bright colours! Any colours you want. It can even be all the colours, but two work fine too. You can blur their edges together if you want. Then lower the layer opacity to 50% ish, mess around with it, set it to Overlay, and then colour under that layer without ever taking the layer off. It'll make all your pictures really colourful, and often can unify their palettes if you only ever eye-drop colours that are already on the page instead of picking them off the wheel. (although be aware that you'll have to colour using very dull base colours or else the whole thing will turn out rainbow-bright. If I had to recommend doing anything, I would do this one! It's so much fun and it can change the way you paint. Do it now even!
here are some useful deviantart tuts and references! the tutorial section on dA is definitely your best friend.
http://fav.me/d7jq1c7
PK's big colour thing
http://fav.me/d31xj5t
ililaz's super subtle method
http://fav.me/d4mij0s
my botched attempt at doing the thing I mentioned in 3)
http://fav.me/d7ykimn