Depends on the rock. If you get it form a LFS then you'll have a change to inspect it before purchase and determine what you'll need to do. If you go mail order, the expect the worse and you won't be disppointed. My two orders of LR were drastically different. They both had good and bad, but the second order took a great deal of curing of being precured. Make sure that you and your vendor understand what "premium LR" means and pay the extra $$$ (my 2 cents). I'm not saying the rock was bad, just diferent and somewhat not what I expected.
LR is great for cycling a new tank. While in the tank, install a mechanical filter and skimmer on the tank. Wash the rock frequently with a powerhead. The mech filter should remove most of the goo in the water (I wouldn't do this if you have a UGF). You may have to replace the filter a few times. BTW your water may get kind of stinky
. When the water have "cycled" do a 50% water change. Wait at least another week checking the water quality (patience is key). If the water is good you're ready to go.
Joe