Making sure your car is up to date on all the maintenance is the best hing you can do for it. Beyond that, I would say wheels, tires, suspension and then tie bars. Im not much into "looks" changes without a function behind them, aftermarket headlights and such might not actually provide more or better light without just blinding others. If you want better lighting, a retrofit kit with high quality parts is probably the best option:

Wheels would be at discretion of style, size you want. I would go with used wheels before hubcaps. A light weight set of wheels off a VW would not only look better, but will help performance with weight loss.

I find Tires to be best for performance and longevity when in the 300 tread wear range with a tread designed for your area and usage (highway, or rain). I tend to choose an aggressive V tread pattern. A little wider (not too wide for rim) and chasing the sidewall to keep the diameter correct. Brand, etc don't matter to me much after that, I have run enough cheap tires to feel comfortable with trying the non name brands. I tend to wear them all out about the same. And have not had any of the separation, or other issues that big name tires try to scare you with.

A slightly lowered suspension won't only drive better, it will allow you to push the car a little more, and be more stable on the highway. I tend to go low, but a decent set of springs even without much of a drop will improve suspension performance.

If you want to lose the body roll and really hang in the corners, a Strut tower bar and rear tie bar are excellent to tighten up the car.