Since I'm not actually that good at drawing -yet-, I only feel comfortable giving these 3 small tips:
a) Don't feel ashamed for using reference material, in fact, RELY HEAVILY ON REFERENCE MATERIAL;
b) Find the software you feel more comfortable with using, and learn as much of it as you can; and
c) While it's good to be a little hard on yourself, dare to submit despite the mistakes you see in the piece. This last one, IMO, is the hardest and slowest lesson to learn - I'm still working on it myself.