1. The first and most important tip, remember, EVERYBODY CAN DRAW, ITS  JUST BELIEVING IN YOU ABILITY.dont let anybody tell you that your work isn't good enough, art is based on opinions, and if you look back at a lot of well established artists their work, could have been drawn by a 5 year old. 
2. NEVER, through any work away, even if you hate it, and would hate for anybody with an artistic mind to see it, keep it, because you never know what you could make out of it, experiment with work that went wrong, layers, different materials, etc... after you have experimanted, if you still fdont like it, dont through it away, make a small paper frame and draw a section of the work, you never know it could be spectacular, and if not, still keep it, bacue if nothing else, it makes you look like you have more work, even if you dont display it...(or even let it see daylight).
3. Always, relate your work to a famous/ or not famous artist... Artist refrences are a BIG, part of AS art, actually comign to think of it, they are a big part of GCSE art as well... when doing your work, if you get stuck, have a artistic block, look at work from other artists, copy there colour scheme or technique, you could even copy the peice, and use a different technique or a different colour scheme, Again remember to EXPERIMENT.
4. If you are stuggling to create, or blend, or just simply dont like the peice of at... Leave it... leave it for and hour or 2, go get some other work done, come backto it after a period of time, and i bet you like it more than before. The reson you are begining not like your work is probably because you have been doing the work for so long, you've been looking at it for to long.
5. REMEMBER good art is in the eye of the user, you dont have to get everybopdy to like it, if you are happy with your work, then forget aboueverybody elses opinion. But do also remember that everything.... absolutley everything, CAN be inproved, but not Everythng needs it, do over do it, if you are happy with some work, but thinksomething is issing, leave it, ask somebody else (your art tutor for example) and see what thay say, you never know just by leaving it you may be improving it.

Blow is alink to a very useful website, watch the videos, you never know you might learn something new: