You can do normal planks, you can do push - up stance planks or you can do planks on your knees if you're just starting out. (chriscoulsonfitness.com)
While your forearms are supporting your body like in normal planking, your body, from your shoulder to your buttocks must be at almost completely horizontal level instead of the usual slightly inclined stance. (adamkempfitness.com)
If you are up for a challenge, try switching from a side plank to a normal plank and over to a side plank on the other side, slowly. (fitnessandpower.com)