Tempo And Rhythm
There's no such thing as the perfect tempo. Ideally each of us should adopt a swing speed that is consistent with our overall temperament. Lanny Wadkins swings quickly, but Lanny does everything quickly. Ben Crenshaw is a more deliberate person, and his swing is slow and smooth.
So suit yourself - But whatever tempo you adopt, be sure that you keep it consistent throughout the round. Try not to speed up when the pressure is on. If you find yourself quickening, then consciously slow things down - slow down your walk, your speech, your club selection.
As for rhythm, there is an ideal, but it can't be described in print. It must be absorbed. The best thing to do is to spend several minutes watching the swings of players with great rhythm, guys like Seve Ballesteros, Tom Purtzer, Larry Mize, and Nick Faldo. Then walk - don't run - to the course and try to mimic them.