The first rule of holding your camera is that it should be steady. This will ensure that you get sharper pictures in lower lighting situations, and that your pictures are sharper in general.
If you’re using a dSLR, put your left hand below, supporting the base of the camera, with the index finger and thumb positioned to adjust focus/zoom. Support your left elbow with your chest and grip the camera body firmly with your right hand, positioning your right index finger above the shutter release.
Posture is important too. Stand firm and erect with your feet spread apart a bit. Do not lean forward, this will make your stance unsteady. Standing straight and with good posture will also reduce strain on your back, especially if you’re carrying a lot of gear.
Do you have other tips on how to hold your camera? Drop ’em in the comments.