Begin from the “up” position, i.e. with your body raised off the ground and supported by your arm.
Keep your back straight and do not twist your torso at all when you are raising or lowering it.
Keep your feet apart. If you want to increase the challenge, though, feel free to move your feet in so that they nearly touch.
Take your off-arm and rest it on the small of your back.
In a resting position, the elbow of your supporting arm should be slightly bent, not locked.
Let your body move toward the ground. Be sure to control the movement as much as you can. It should be slow and deliberate, not strained or jerky.
Continue until your chin is about a fist’s width above the floor.
Now, with all your might, push your body up from the floor to the starting position. Make sure to keep your back straight and to stop just before you “lock out” at the elbow.