The rules are: There are no rules! What's more important is what works for you. I personally like my snare and floor tom totally level and my two rack toms slightly angled toward me. Keith Carlock on the other hand has his floor toms angled AWAY from him and his ride cymbal almost covering up his rack toms. What is most important is: Can you keep steady time? Can you accompany other musicians without overpowering them? Can you make it swing? Set up doesn't matter if you have the talent to really play!