HOW TO - do a Cartwheel

A useful aid in teaching/learning carthweels is an AAI cartwheel mat.

Make sure you have plenty of room. Allow enough space to perform the move. It's also best to learn and practice on a softer surface such as a mat or a well-padded carpet.

Decide what kind of cartwheel you are going to do. There are two types of cartwheels: front to back and side-to-side. The directions here are for front to back. Front to back cartwheels are when you start facing one way and end up facing the other way. In a side-to-side cartwheel, you stay facing the same direction throughout the cartwheel. Starting forward works better because that is the way you will be starting for your roundoffs later. When doing a cartwheel make sure that you have the upper body strength to go over.

Extend your arms straight above your head. Don't bend your arms and keep your hands turned in towards your head, with your arms against your ears. Reach for the sky!
Point one foot in the direction you will be going. Turn the other foot slightly outward, for better balance.
Look down at where you are going to place your hands.

Reach with the same hand as your pointed foot. For example, if you pointed your left foot, use your left hand until it touches the floor. Your other hand should follow. While the first hand is going down, the opposite foot is coming up. Keep both hands in the same line that your feet started from, and your hands will point perpendicular to that line.

Kick powerfully so your legs come off the ground. Now you are balancing your weight on both of your arms, like a handstand, with your legs straight in the air and out in a straddle/split position. Keep your back straight. Think while you are doing it with this method - Hand, hand, foot, foot!
Look at your hands. Keep them super straight, firm and balanced. This will help keep your body in control and will aid your aim, agility and balance. Keep your trunk in a straight line from shoulders to hips. You should be turning in a position reminiscent of the spokes of a bicycle. If you're not, then try again and again until you get it.

Land on the opposite foot. Do this facing the direction you came from, front leg slightly bent. This should be the same position you started in, but with the opposite leg forward and both feet flat.
Straighten out. You are done! Then smile and show it off to your friends.

http://www.wikihow.com/Do-a-Cartwheel