If your slice float too much, try to take the racket back at the level of the ball, and hit through. Once you get the feeling of hitting through and slicing the ball, Take the racket back a little higher.
Also, keep your weight on the front foot, and keep your chin down.
Also, you should be able to draw a straight line from target to your hitting shoulder to your nondominant shoulder, in other words, stay sideways.
For me, it helped to think to meet the ball with outside of my hand and to push the ball with outside of my hand as long as I can. It may work for you, or it may not.
If you want to add a bit more knife to your slice, keep your elbow up as well.