There is a TON you can do, but the very basics are...wel let's jsut link to a "guide" that kind of explains each setting.
http://forums.mozillazine.org/viewtopic.php?t=53650
That one is pretty good, explaisn alot.
More reading -
http://www.linuxjournal.com/article/8004
I jsut use a program called "FasterFox" that "does everything for you". From what I can tell, it tunes it jsut as wel as I could in a fraction of the time. At first its fun to mess around with but after a while I hate re-setting everything and FasterFox does the job well enough.