Body Surfing can be great fun if learnt correctly.
There are 2 types of techniques you can use to catch a wave body surfing. You are either standing on a shallow sandbank or swimming in deeper water.
The first technique of standing on a sandbank in shallow water is the easiest to learn and first step you should attempt when learning to body surf.
To catch the wave you need to be standing upright. However, if the water is above your hips this technique wont work.
Wait for the wave to be right behind you, then as the wave hits you, dive with power over the water and land on the surface with your hands stretched out and head down. This stream-lined technique should hold you on the wave, however your weight needs to be on your hands and not on your feet.
If you are not catching the wave, your timing is probably out. Just practice until your timing is right.