5 inch sand bed, nasarius snails, sand sifting stars, sea cucumbers to keep the sand looking clean and aerate it.
PVC rings to support rock and sculpt around it with more rocks. Start with the big rocks, create a hollow centers that allows for very good flow even in the midlle of your rock structure (limits deadspot where detritus might build up if you don't have a good detritus crew). also good hiding place for creatures , crabs, shrimps and other scaredycat monsters...etc...
as others have said, whatever makes it fun, after all you'll be the main one looking at it everyday and cleaning-up