There's no secret, but it will take a little experimenting to get something you like. Bouncing flow off the glass and rocks help spread things around. They don't need to be pointed directly at each other, but having their flows collide into each other help break up any circular motion, and that's a good thing.
I know it's hard when you're starting out, but also try to visualize what type of corals you might have in the future, and where they might live. Some corals like high flow (usually corals that want to live high in the tank) and some like low flow. Try to plan your flow accordingly so you have some high flow areas and some low flow areas. Yeah... it's tough, but just go into it realizing that you'll probably move those powerheads around 3-4 more times as you start stocking your tank with coral!