The best way to start is to check pictures of the real thing to make sure how it should like. T-34s had bent fenders up front and many pictures show them with the front fenders missing. The fenders towards the rear are mostly untouched.
In terms of dents and dings on the fenders this is what I do. First i take sand paper and thin the heck out of fenders as much as I can. If you have a motor tool its even easier. Than its just a matter of using pliers and bending the thin plastic. For bullet holes I simply burr a hole in with an x-acto knife. Of course, if you have the means and ways just replace the fenders with PE. Just as an aside, back in the day when I started modeling (not that long a go) I would simply bite into the fenders with my teeth and bend it. VERY BARBARIC!!!!
For holes created by rounds that hit and skipped the tank surface I heat up the sharpened point of a pencil and create the dent on the surface. It leaves a pretty accurate shape. I do all my battle damage before painting. Hope this helps and that your T-34 comes out really nice!
Cheers,
CDT Reimund Manneck
U.S. Army ROTC