Eight, or is it 9, videos on the serve.

This is the most complex and difficult to master stroke in tennis, but you don't need anyone else to practice it.  You can just go to the court with a bunch of old balls and swing away.  My advice is to ignore the service box don't worry about hitting the ball in, try and hit your serves correctly, once you're hitting your serves correctly the ball will be going in (with depth, pace and consistency).