I would get a KN air filter (just the filter, dont spend money on an aftermarket pipe), shifter bushings (if its a manual), some lowering springs (shocks too if you have the money), some nice rims that arnt too flashy (no bigger than 17''), and finish the car off with a front lip. This will make the car look and feel sportier without looking cheesy.
Do NOT buy a body kit, wing, 19'' rims, huge muffler, or a bunch of stickers.