If adding them to a new set up that has no livestock in it, there's really no prep to do, unless they have something growing on them that you don't want.
Just rinse/swish them around in a bucket of saltwater before adding them to the tank and you should be good to go. There are a few products out there for cleaning LR such as 'Kent Marine Rock Prep' that you can use, too.
I would do the bucket of water thing unless its really high quality rock to get some of the crappy die off first so its not just in your sand bed for eternity