Find a space in which to do a back flip. The space -- preferably a gymnastics gymnasium - should have high enough ceilings and enough space around you so you can freely move without risk of bumping into something. You should also have an adequate gymnastics mat on the floor of the space to help minimize injury in case you do the back flip incorrectly or fall.
Stretch your body before doing the back flip. Stretch out each leg and both of your arms. Perform neck rolls, shoulder rolls and torso twists to loosen up your spine and the rest of your body.
Stand straight up with your feet planted firmly on the ground shoulder-width apart. Swing your arms back and forth from your side up to above and behind your head. Continue swinging them until your arms have a momentum and rhythm going.
Bend your knees slightly so you're almost in a squat-like stance. Continue to swing your arms, and when they are both extended above your head, jump off the ground with both feet in an upward and backward motion. Bring both of your legs up and tuck your knees so they are against your chest. Don't arch your back. Place your arms either in front of your knees or behind your knees when you reach the maximum height of your jump and your body should flip around.
Stretch your legs outward so they are approximately three quarters of the way extended. Keep your legs slightly bent as you land on the ground and put your arms out at your sides to balance yourself.