From a new trail rider's point of view, I would point out that a stock Jeep is a descendant of a military vehicle and is really very capable with _no_mods_whatsoever_. So don't worry about mods, just go out and wheel it.
The very first mod to my TJ was a set of tire deflators and a decent cheap air compressor to run off of the lighter plug. My first offroad adventure was some mining trails in AZ, a side trip from a "normal" camping trip. Totally stock, I just aired down and tried it. The jeep had no problems, and was way more capable than its driver. Airing down helps on every obstacle, every trail, every rock, every bump. I recommend it for a first "mod."
Similarly my TJ came to me with BFG AT 31" when I got it, and having tires that are meant for off road, really matters everywhere. Every foot of trail will touch your tires. So get good tires early.
My first real mechanical modification to the Jeep was anti-swaybar disconnects. The extra flex you add to the suspension by simply disconnecting the swaybar is useful for every obstacle big or small. The softer ride from airing down and disconnecting, makes for a more enjoyable ride on the trail too.
Lots of other mods are useful, but in specific circumstances ... A couple inches of lift, a locker, a tummy tuck, nerf bars, tow bumpers, I have all of these too, and I like them. But for a new person, I would start with good tires, aired down, disconnected swaybar -- these mods I have found most useful on every trail, all the time.
--Ron