Something simple I have learned very late in my time gaming is to write page numbers down. Spells, skills, abilities, seldom-used resolution mechanics. Any time you have to reference a rule, note it on your character sheet. I prefer this to the printout for two reasons.
The first is that it allows you to create a list of bookmarks based upon actual play in real-time. If your information is not on the printout, you still have to break out the rulebook anyway.
The second reason is that it allows the group to help. If you're engaged in a dramatic moment, the last thing you want to do is thumb through the rulebook. One of the other players can easily flip to the appropriate section with a page number. Or, in situations where the rules are called into question (our memory is never as good as we remember it to be), the entire group can look along and provide insight as a ruling is reached.