Try doing push-ups with your hands about shoulder width apart, and turning your elbows as you bend down so that your elbows touch your waist. Your fingertips should remain facing forwards (don't turn your hands out), and don't let your elbows in so much that your stomach rests on them. You should be able to almost touch your chest to the ground and still have your elbows touching your side.
Your body should remain in a hollow body position (do not arch) as you go down and as you push back up. For an added bonus, if you push your shoulders out hollow at the top, you will work your shoulders and deltoids.
(1) Once you're bent down, hold that position for 5-10 seconds before pushing back up. Remain hollow. (2) Bend your arms only half-way and hold it for 5-10 seconds. (3) Elevate only your feet a foot or so off the floor (using mats or small blocks). Be sure your shoulders remain over your hands. This will transfer more weight to your arms as you do your push-ups. (4) Do these push-ups with your feet and hands on the beam. (5) Do these with your hands and feet on the parallel bars (one hand and foot on each rail).
Get into a hollow push-up position with your hands on a low beam and your feet on the floor (you should be cross-wise with the beam). Your shoulders should be over your hands, back flat, tummy in, and bottom squeezed. Then all you do is bend your arms until your chest is an inch from the beam (don't touch it with your chest!), then push back up. 10-15 is a good range to begin at, but then aim for 20-25.
As these get easier, find a lower beam (or put your feet onto a mat). Soon you will be able to do the same number on the floor.
An alternative that works slightly different muscles would be to turn your hands around so that your fingers face away from you. The hand placement for this is easiest to do on a low beam.
These can also be done on a single rail, where you begin in a front support. Keeping your torso and bottom squeezed tight, bend your arms so that the bar touches your rib cage, and then straighten your arms and round your back so that the bar touches the middle part of your thigh. Repeat -- sets of 10 or more.
Handstand Shoulder Shrugs
If you are stronger/more advanced, this can be done on the uneven's low bar without you sitting on anything and starting from a pike hang.
More advanced alternatives to this would be to pull your chin over the bar and hold yourself there for 10-15 seconds (again, no resting your chin on the bar!). This hold can be integrated into a set of 10 pull-ups (every 5, for example).
This is a good lead-up exercise to handstand push-ups.