TMAD4

So im not stupid or anything when it comes to cars, but i just got an 89 gt, it has flowmaster mufflers but otherwise is stock. Im not sure where i should start for performance upgrades. I would like to put higher gears in it, but im not sure what i should go with. I would mainly be screwing around racing people on the streets. and obviously a cold air intake and the rest of the exhaust. but what about maybe like a bigger throttle body and underdrive pulleys? i think id rather do that than go with a turbo or supercharger right away. I just dont know what would make the biggest difference.