For butterfly, I can't help, I'm not 2 great at it, but freestyle is my best stroke, so here are some tips:
1) Kick very hard, but be careful not to bend your knees. Kick from your hips. Also, it helps to rotate a little.
2) It also helps to breathe every 3. most people do this already, but just in case. :)
3) Look at the bottom of the pool, not in front of you. (I know this sounds stupid, but you wouldn't be looking completely downward, just angle your head down)
4) Cup your hands, and really PULL the water. This is probably the best tip ever. It helps so much, and it makes your stroke look beautiful from above. This really speeds you up. To practice pulling the water, use hand paddles, which you can find at kiefer.com. That's where I got mine, and they work very well.