All solid advice thus far. I would just reiterate what VJ said by adding that sometimes it helps to change your paradigm; use your legs to manipulate your opponent by squeezing your knees together and pointing them left or right. When you do a crunch, you can look at it as your torso moving to your legs, or you can look at it as your legs moving towards your torso. Equally valid viewpoints with equally valid applications to the game. You can also pull outwards on the opponent's elbows as you pull with your legs.