DOs:
Make sure the new live rock is fully cured.
Remove a few galons of water before adding the new rock as the extra rock will displace some water. Then use the removed water to top off the tank after aquascaping.
I like to bury some of the rocks down in the substrate to provide a good stable platform to build my rock up.
Place the rock so that there is room for water/fish to swim in and about the rock. Try to not place the rock up aganst the side or back glass.
DONTs:
Add live rock thats not fully cured.
Stack the rock in such a manor that its like a rock wall.