Full bult-ons would be a good start. exhaust (headers, midpipe, catback), gears, cold air intake, throttle body, under-drive pullies, short throw shifter, chip, to name a few easy ones. Check the tech forums and street/strip, see what other people have done and you'll get an idea of what you want fairly quick.
Welcome to the forums, have fun, AND TAKE NISSAN OFF THE FRONT OF THAT MUSTANG!