I just walk off the edge, keep legs together and arms at my side. Sometimes I do a lifeguard entry, which is jumping with legs spread front to back and arms pependicular to sides. I close up arms and legs before entry, but this is a stable way to jump for me. Of course, the lifeguard jump is designed to leave your legs and arms in this position so that when you hit the water you don't go under and lose visual on your victim, but I don't recommend this at 40 feet. Xtabi is a good place to get your feet wet with cliff jumping BUT DO NOT DIVE. I hit bottom on every jump, so diving would not end well for you. I jump off Xtabi with snorkel gear in one hand a live waterproof video cam in the other, no problem. People get hurt at Rick's when they:
1. Over rotate-that means you have too much forward momentum and your body is obeying the laws of physics. Big running jumps usually lead to this. Which means BELLYFLOP! It doesn't take much of this to get you a good WHACK on your belly.
2. Under rotate-that means that for some reason your weight shifted back while jumping and you will land on your butt or back.
3. Side rotation-that means that for whatever reason, you did not exit the cliff straight ahead. Usually due to visually focusing on an object or scene that is either greater or less than 0 degrees in front of your body. Keep your head straight and look at an object in the distance that is 0 degrees in front of your body. This one usually ends badly, I've seen blown eardrum and worse.

If you've had back issues, disc surgery, hip or knee replacement, neck issues, sinus issues, heart issues, kidney issues or other health issues that could be adversely affected by an almost 40 foot drop into water, forget it. Life is too short. That said, I love cliff jumping and Tam does too! She got her start at Xtabi.