Thanks everyone!
I've been handpicking rocks from different sources (all fellow reefers, saving me a lot of dough), usually just a few at a time even though I know I need more. I keep looking for oddly shaped rocks that have lots of nooks and crannies and holes and stuff, and rocks of varying shapes from round to flat. And then trying to stack it to create caves and holes. I'm trying to give fish hiding places but also create holes and shelves to place corals. The hard part though is the tank is small so it doesn't leave me a lot of room to mess with placement front to back and it's a bit more vertical of a slope than I would want.
Anyway, I'm going to try to pick up some more pieces this week from rubble size up to about 4-5 inches. :)