As mentioned above, proper camera holding techniques will help you out quite a bit.
If you're using a DSLR, support the weight of the camera with your left hand at the base of the lens, with your left elbow braced against your body for stability. Use your right hand for aiming and control, never to support the full weight of the camera.
Here are some other things to try:
If all else fails, use a shutter speed that will minimize the effect of camera shake - the general rule of thumb is to use a minimum of 1/focal length (e.g. minimum of 1/200 for a 200mm lens), but you might need to double that if you're particularly shaky. A lens with good image stabilization will help a LOT. (Canon calls it IS, Sigma calls it OS, don't remember what other manufacturers call it)