I'm about to drill a hole into the trem cavity of my prized Ibanez RG1570 in order to install a hipshot tremsetter, having never drilled anything before in my life. Is there anything I should know before beginning? Maybe a website to recommend that I could read through?

Cheers, appreciate any help.
I would suggest trying it out on something before you butcher your axe.

EDIT: You want to keep the drill perpindicular to what you are drilling, and apply pressure otherwise it wlil jump around.
use a drill press if possible, also start with a drill bit smaller than the hole that you need, and work up to it, this has two benefits, 1 its more accurate, and 2 the smaller drill bits jump around a lot less, so there's less chance of a huge gouge in your guitar, and once you have the first hole drilled, it provides a pilot hole for the next size up and so on...

"You're a MESS!"
If you cant use a drill press, get a friend to check whether you`re drilling pretty vertically, and like Liquidstate said, use a smaller bit as a guide