research and more research...
many people neglect the power of the search button...
when i first got into DSM tuning i was all up on it for like the first 4... wait i still do it all the time! this site is my mainstay, although i have not really been too much of a player like i used to be. RKO is also a wealth of superlative knowledge. the AEM forums are a good read [mostly EMS related, but still great deep tuning info].
mostly i studied the 'upgrade paths' like crazy. find out what people are upgrading and you will also find out why. along the way you will pick up the other stuff that gets tacked on [stories and the likes].
as far as general automotive knowledge i just picked it up along the way. i'm always thinking of how i can tweek things. having a somewhat analytical and creative mind also helps. having the 'can-do' attitude is great too. but most importantly try to find out by yourself before asking a question. then bring the evidence you have researched to the front so you will have an intelligent question to follow it. this will also lead you to mostly finding out your own knowledge.
oh ya, and go take a good look at your enine, its all basic stuff...
suck squish bang blow