I'm a cheerleader in school and I really want to learn how to do those
things. It's really hard. Can you give me advice?
Let me preface everything I'm about to say by telling you I am crap at anything gynnastic-like. I dropped out when I was six because I was afraid to do a cartwheel; I didn't want my feet over my head.
That being said, I think anything physical is easiest when you are in top condition. That means eating in a healthy way, getting regular moderate exercise, and getting enough sleep.
I also think practice is the only way you're going to succeed. This means realizing that you'll fall, bump your head, and graze your knees. Think of a little kid learning to walk - they are on their butts more often than their feet, yet as adults we're all walking around with no problem.
I'd suggest asking your cheerleading coach for some extra help; you can also ask other girls you feel comfortable with. Of course, if you have spare time, joining a gynastic club can do wonders. They'll focus solely on your tumbling - making you a better athlete and cheerleader.
Good luck!