Originally Posted by rkelley
If I want more topspin then I direct my swing path to be more vertical.
Not that this is false, but your swing path has a greater influence on the ball's flying increment than on its spin.
If you want more spin, without changing anything else, close your racket face a bit. The idea is that you'll get to make contact above the center of the ball with a closed face, meaning that the upper edge will get accelerated forward. As you swing a lot faster forward than upward -- I've rarely seen pros going beyond 30 degrees of swing path prior contact, including Nadal on clay -- you'll get more spin that way.