Welcome to the crew. I guess starting mods depends on what you plan for the truck! If It were me, Id get new wheels and tires. Dont get big tires unless you can gear it right though. The reason I say wheels is because they say alot about the vehicle and the owner. They set your rig apart from the crowd.
If your rig looks stock and you want it to be noticed, wheels all the way. I personally did performance things like chip, K&N Cold Air(noisemaker), exhaust, etc. But now that I bought my new wheels and tires, I know that they made my vehicle.
(they arent the same black wagon wheels that are in my avatar by the way, they are black teardrop style wheels. They're rapped in Cooper Cobra's, with 245/60R15 up front, and 295/50R15 in the back)