If you are new to comics art, start hanging out at the Critical Mass forum. We post projects for everyone to draw and post, and then we critique the results and you can compare your art with everyone elses. Vegeta has been haning out there since he registered, and he is improving by leaps and bounds. You will too, if you participate.
Aside from that, find a copy of Drawing Comics the Marvel Way by Stan Lee and John Buscema. And Understanding Comics by Scott McCloud is another must have for understanding the philosphy behind comics. Both of these books are essential to comics artists IMHO.