You have an experienced coach? Listen to him/her.
Unless you have reason to distrust them, an in-person experienced coach, someone who's coached for a while and competed with years in the sport is the best source of teaching.
Sounds like you're new?
THe jerk issues mostly sound like practice will fix them. The flexibility issue, well, listen to your coach, and give it time. I know my flexibility continued to increase for a long time so that now I require little warm-up to hit deep positions.
Stretching resources? Try Pavel's books, I hear they're top.
Oh, check with your coach.
"Morning, Putski eats it, noon, Putski eats it, night, Putski eats it. Putski loves!"