The slice shot (when the ball curves left to right for a right-handed golfer) in golf is one of the most common swing ailments. The slice most commonly occurs when the clubface is open relative to the swing path and/or when the swing follows an “out to in” or “over the top” swing path.

Anti-Slice Drill-

Many times a slicer opens up the shoulders too quickly on the downswing causing the clubhead to tip over and cut across the intended target line. This path, of 'outside to in', combined with an open clubface at impact will cause the ball to spin from left to right.

To counter this move, try hitting some shots with a closed stance.

Use a club as an alignment aid.
Set up to hit a normal shot where your stance is 'square'.
Slide your right foot back, so that the toe of the right foot is in line with the heel of the left foot (for the right-handed golfer), thus closing your stance.
Swing back normally and hit a shot.
Closing your stance will do a couple of things: 1) will help you create a more powerful turn and 2) a closed stance will help the club path to stay more on line of even a little inside the line so that you can rotate the club through impact and hit a shot with more 'right to left' spin.

Watch the video to see how to do the drill.