I'm running a Rough Country 2" front leveling kit with 285/70/17 Nittos. I also have some 3/4" rear coil spacers just to lift the rear end up a hair, but I haven't installed them yet due to lack of time. Also have an Airaid Jr intake kit which is a great way to go since it retains the stock airbox. Lstly, I just got a tune done by Justin at Black Bear Performance, and holy shit. Best money I've spent on the truck so far.
So, I'd start with intake, leveling kit, tires and tune...although not necessarily in that order depending on your wants and needs.