Summarize this article:

This will help your body feel limber and warmed up, making it easier to planche. Proper stretching is a vital part of avoiding preventable injury. A planche is an advanced technique, so you'll need your body in its best order before you attempt it.  Touch your toes. Keep your legs as straight as possible. Circle your wrists and hips. Stretch your arms by Crossing one arm over your chest and holding the elbow with the opposite hand; repeat on the other side. Crouch between either push-up bars or parallel bars with your hands grasping the bars on either side. If you don't wish to perform the planche on bars, squat down on the floor with your hands planted on either side of you. Make sure your hands are planted a comfortable distance apart, so you'll be able to support your body adequately. Placement of your hands during a full planche is extremely important to its success. Before you lift yourself up, make sure your hands are planted facing forwards, roughly parallel to where your belly button will be when you lift yourself up. Experiment with different hand grips before you find one that works best for you. Tightening your body will help ensure your body's trunk is firm throughout the planche. Because proper balance is so important during the planche, you need to keep your body straight. Tightening in your abdominal muscles will help keep your body rigid.

Summary:
Stretch first. Get in position. Plant your hands directly below your navel. Tighten your abs.