The excellent Advergirl has started a series of tips for beginners in the ad industry. This is an excellent idea - and a service that the ad blogs don't tend to do much of (Russell's APSOTW being the huge exception).
Her first piece is the immensely helpful AEs: this is your real job description. It includes a cheat sheet. Even if you're not an Account Exec, if you deal with clients in any way, go read it.