Quote Originally Posted by Zeful View Post
Just a quick question, how do you know what to take notes on?
Anything you know is going to come up in the session, or is reasonably likely to, even if not certain.

That, and a small set of "contingency" plans -- general-purpose creatures/NPCs/locales, etc., for when your players do something unexpected. You won't use them every time, but when you do need them, you'll be glad to have them.