However you want. But remember it's a wave not a salute. I just raise two fingers, index and middle, on whichever hand is on the steering wheel. I have gotten some pretty enthusiastic waves though if that's more your style.
2014 JK, auto, MC GCL 2.5", 35x12.5x17, 4.56s.
My observations are based on my experiences...YMMV.
Before I moved, my buddies and I used to do that. We also had some other hand gestures we would use A few times other Jeepers who were around would see, and give us the dirtiest looks. They really thought that we were serious.
We also used to block each other in, in parking lots. Like, I would spot my friend who was in a store I was going to, and if possible I would park as close to his drivers door as possible, so that he couldn't get in. Then I would take my time in the store if possible.
Oh yea, and related to this thread. I used to be the "hand out of the Jeep" waver when I had my YJ. Now I keep to a "wide five finger wave" most of the time with my XJ. Most people don't wave at XJs, except other modified XJs, which is fine. I understand.
I was told, when I first got a Jeep, years ago, that you gotta think of it like you are waving at the Jeep, not the driver. Because then it doesn't matter if you don't get a wave back (which happens a TON with JK drivers.)