In the process of setting up my tank, I had more fun positioning the rocks than with anything else. But thats just me. The only suggestions I can offer are that you should get about another 50 pounds or so of LR for filtration. IMO the tank looks barren with the amount you have anyways. As for the rocks you have now, push your base rocks down through the sand so they're resting on the glass. Try to partially think of it as tetris. By that I mean spin the rocks around, turn them upside down and try to "fit" two or more together to make not only a visually pleasing structure, but also one that has lots of holes and gaps for the fish to swim through. Also, try to keep as many points of contact between rocks and glass, and rocks and other rock to keep it as stable as possible. If you're really imaginative, you can also try to position the rocks in a way that will help manipulate the flow from your powerheads to your advantage instead of causing dead spots (tis should be a breese if you aced the vector units in Physics class). Its easier to move a few rocks around now and save yourself having to buy and extra powerhead just to get rid of a dead spot.
Heres a picture of my tank. I spent a good hour going through all the rock at my LFS to get the best shaped ones. I was even lucky enough to get one that was already shaped like a shelf.
