Where/how to place corals?

Is there a source that can tell me where to place various
corals/anemones to best effect/security? Or should I just plunk them
down in various spots? I can see on various sales websites that some
that need more/less light, more/less current, space/not, so that would
lead to some placement guidelines. I also know that anemones can move,
so they can adjust their own placement. But should I put corals on my
live rock? On the sand? Horizontal? Wedged in a crevice? Does it depend?

I ask because I bought my first coral (about a 3" circle of polyps) and
placed it (I thought securely) in a corner/crevice of some rock,
thinking it would anchor. After it fell over/off the third time or so,
I've now moved it to a level surface on the sand. I wonder if every
coral is going to be different, and how to find out. I also don't want
to end up with everything just sitting on the sand, or eaten by my sand
critters...

Thanks!
Scott