First of all, you should not overcompensate. It is noticed that some golfers make a rough estimate of the distance of their slice and then make a left movement accordingly. They do that, thinking that they are aiming to the left of the hole. The point is that by aiming to the left, the ball will sail towards right and fall into place. This is like trying to fix a stab wound with a Band-Aid; it doesn't fix the problem in any case.
In fact, you should try to stand with your feet shoulder-width apart. Your form before the swing can either set you up for a straight shot or a slice. Your feet and shoulders must be lined up before your swing begins.
Make sure your club shaft reaches its peak over your shoulder, not your head. Do this by noticing your left arm as it crosses your chest. To lower the top of your swing, make sure your left arm touches your chest on the backswing more than usual.
Keep your wrists straight on your backswing. A golfer who moves his wrists increases the odds of slicing. By keeping your wrists straight, you help ensure that the club hits the ball in the proper position.
Imagine another ball about 3 or 4 inches in front of your ball. When you make contact with your ball, try to "hit" the imaginary ball as well. This will help keep your swing straighter.