you may have to play around with it a bit till you find something that is pleasing to your eye .Aquascaping is one of the more personal prefrences of this hobby.
I have taken the bigger rocks in mine and built it up with the smaller peices . Leaving lots of nooks and cranneys to allow the fish to hide as well as allowing for future pieces of corals. If you pick some intresting pieces they should fall into place like a puzzle for you. If you find that they dont fit "right" dont be afraid to use a hammer and screwdriver to chip it into a shape you like , I have even drilled holes through mine for an arch effect , it will make the water a bit cloudyier and take a bit more time to clear up but no worries there . Hope this helps ya out. BTW :welcome