Most of it is just learning the timing and positioning on how to do it. Additionally, as the rally gets longer the hits get faster as well. In all honesty, hitting well is probably the highest skill floor in the game when you account for Dive Assist being part of the game. You have to have good timing, good movement, good positioning, and doubly good at your aim (avoid blocker and put it where dive assist can't get to it). For the most part, though, as long as you're not right on the net most angle hits work once you get the timing down. The more advanced stuff is very high risk and low reward.