Both my 00 TJ and 05 LJ would average 14-15 mpg. LJ was stock, the TJ is lifted 2.5" on 31's. The only thing you can do to improve it is make sure it's tuned up and running like a top, slow down and don't race around. No mods will get you better mileage, so don't waste your money, so just stick to stock.
"Anything to do with the land, I love."
"So it's probably eighty percent luck and twenty percent skill."
I never could figure what the sky was thinking, but the soil, she don't keep too many secrets.