I'm a paranoid feller, so perhaps i'm overly cautious. I have a bunch of base rock that I use so I find a good cut piece with a flat side and lay it directly on the glass. I do this with a couple large, well balanced pieces to establish a base to build up. Once the "first layer" (bottom level) of rocks are placed, I put sand in and pack it around the rocks for a good, solid base. Then I check to make sure no pieces "wobble" too much. Then place some more base rock or live rock on top of the first layer and so on until I have many caves, crevaces, and a few "open" areas surrounded by rocks.
If I put a piece of live rock on the bottom (I like live rock closer to the light) then I make sure it rests very stabily on sand. My logic leads me to think pods and other creatures that live in sand and rock like a connection that's easy to traverse from one to the other. And live rock usually has no "flat" sides that allow it to rest "wobble-free" on the glass. I never lean anything on the glass too. I like to build towering rock structures that get as close to the surface as possible, so my paranoia is a good thing, considering one off-balance piece could someday tumble and shatter a wall of my aquarium.