I'm not a very good PFTer but here are my tips:
Crunches: stretch your quads before hand. I find if I don't my legs tighten up bad around 75 crunches.
Pull-ups: Look at the bar when coming up. Its awkward and you might start to feel a headache because you eyes will probably cross, but for me seeing the destination makes all the difference (I used to do them in front of a mirror, big mistake).
If you do chin-ups (palms toward face), grip the bar exactly shoulder width apart. I think I lose power when I "chicken wing" in or out. You may also feel yourself almost traveling away from the bar, almost like an arc movement when you go up, as you do it, but you get a more streamlined bicep movement.
Basically just work on you technique for everything. Crunches is where you actually want to shoot for the minimun- minimum amount of movement up and down to achieve one crunch. It also took me about 1000 pull ups to be comfortable with my grip and perfect the "fall" down and catch/spring up method.