upgrading my car.......

okay i want to upgrade my car, but i dont know where to start. one of you guys mentioned new spark plugs, leads and extractors. my first question is, what are leads and extractors exactly and how do they help the performance of my car? and my second quesion is, what else should i do to upgrade my car? any help would be great.

Cheapest way is to take out everything you don't use.