Set-up: Set-up on a soft surface next to a tall sturdy box or household object on which you can rest your feet. Place your feet on the box and incline at the hips such that there is a right angle between your legs and your torso. Make sure you have total balance and stability before beginning the movement.
Movement: Lower yourself as far as you can under complete control, then reverse the movement - using the box for stability at all times.
Emphasis: The key to the handstand push up is control - do not exceed a range of motion you can control.