I do a fairly extensive printout of basic campaign information. A general overview of the campaign, house rules, character creation guidelines, etc.
It's pretty thick because we have a lot of house rules and additions. I list the pre-approved prestige classes (all PrCs must be approved by DM, if they're approved, they're added to the list with any conditions that go along with them), races, recreation policies (i.e. if you die, you create a new character with 80% of your previous character's XP... Raise Dead and such spells are outlawed. The only spells that can bring a character back to life are Wish and Miracle).
I have a page devoted to things I need to know from the character. I want to know hometown, social status, family, and those types of things. I generally allow people to build a character through play, but I want the basics as I very well may use them in game.