For right handers, keep your feet either square to the line of play (see further below for an explanation of line of play) or the right foot a little bit behind the left foot. Keep the feet wide apart - typically a fair bit wider than shoulder width - check out the professionals in action for examples of just how wide they go. You should be crouching forward a little, and your elbows will be roughly shoulder width apart, with the tip of the bat pointing forward.
The basic idea is that it should be easy to hit both forehand and backhand from this position - the forehand by simply turning the shoulders to the right, and the backhand by rotating the forearm 90 degrees towards your torso.
For further detail and diagrams, see the links below.