Study what they tell you to study. Nobody cares if you know how fast the fan spins or how many rivets are in the airplane. Follow the training program.
If they tell you to know your flows, call-outs, limitations and memory items before you show up, know them. You don't have to know why you're touching a switch at this point, just know you have to touch it and when.
Attitude is 90% of airline training. Most training programs will work with you as much as you need...provided you have a good attitude. If the instructor is constantly riding you and your partner and being overly negative, get a new instructor. If it's only you who is constantly butting heads with the instructor, look inwards and knock that s*&t off! It can't be stated enough, cooperate-graduate! If you need help, ask!
Good luck!