My slice was caused by turning my shoulders around my spine (imagine spinning or turning a 'T') - this was accentuated by pulling and pushing with my right shoulder (I'm a RH Golfer). This push with my shoulder caused me to hit from the outside, leaving no choice but to compensate and bring the club back inside - giving an out to in swingpath, causing a slice.

My swing is now reaching across my chest with my left arm instead, letting my upper right arm hang and my right arm fold, keeping my right elbow down. Now I leave my right shoulder 'dead', and my swing path is in to out - and my slice is gone except for when I try to kill the ball (and pull and push with the right shoulder).