1. Support yourself from either your elbow or your hand out to the side. This is demonstrated in the figures above.
2. Make sure your body is straight and your head is in line with your body. Make sure to avoid twisting or rolling your body over.
3. Your elbow or hand should be roughly below your shoulder.
4. Supporting yourself from your hand makes the exercise harder in terms of shoulder stability. Supporting yourself from your elbow makes the exercise harder in terms of core strength and body posture.
5. Try the different leg variations once the standard exercise becomes easy. Lifting the leg adds an extra challenge.