First question you have to answer for yourself: what do you want to add to the rockscape? Are you looking for arches, caves, branches, shelves, etc?
There are different options available from dry rock to live rock to dead rock, etc. live rock is typically more expensive and often comes with with hitchhikers or bonus life of some variety. Depending on where the rock comes from you could end up with good hitchhikers or pests.
If you decide to go with dry rock, depending on if it was previously live, you should probably soak it for a few days to make sure anything dead and decaying doesn't cause an ammonia spike when added to your tank.
I soak mine in saltwater from my tank and add some phosphates to preload the rock before adding to my tank because I have to dose my tank with phosphates.
Presoaking also allows bacteria and potentially some pods to start colonizing the rock before it goes in the tank.
If it's "new" dry rock, a good rinse is all that's really necessary but a presoak still does the same as mentioned above.