Practice the J-step approach, running in a small J-pattern, to get comfortable with the pre-takeoff movement. Using a J-step approach will cause your body to naturally twist before takeoff, so it is very important to get it down.
As you take the final step in your approach, pivot around your front leg, which should be leg on the inside of the J, and swing your arms down toward your hips.
Swing your back leg forward, up, and across your body, like kicking a soccer ball. Make sure that your kick travels up, and not out, or else you will not be able to flip over. Your arms should rise to give your body more upward force.
When your kick reaches the peak of its power, jump powerfully with the other leg. As you do this, turn your head in the same direction that you just kicked toward and wrap your arms tight around yourself, like a mummy. The head turn will begin the 360 degree spin, and the arm wrap will help you spin faster.
When you have completed a 360 degree rotation, spot your landing and land with the same leg that you jumped with. Your kicking leg should come down last.