PREPARATION
1.Kneel on the floor. Lean forward
  and place your hands on the
  floor, well forward of your
  body, palms flat and shoulder
  width apart.

2.Straighten your legs, raising
  your knees off the floor and
  pushing your body forward, so
  that your shoulders are directly
  above your hands.

3.Make sure that your back is flat
  and your head is in line with
  your spine. Breathe out.

EXERCISE
1.Breathe in as you lower your
  chest to the floor. Keep your
  elbows close to your body to
  work the back of your arms.

2.Hold briefly, then breathe out
  as you push up, raising your
  body away from the floor. Do not
  lock your elbows.

Do not rest between repetitions.

MAINLY FOR: Anterior deltoids
            Triceps
            Pectorals

For press ups which work the chest
more and the arms less, see the
exercise "Press Up Wide".