I'd like to give useful advise to Marc Ambinder, who is about to become a White House reporter and is, to his credit, self-aware enough that he's asking how to do it. I'd like to, but because I think he's a good reporter, my inclination is to say: Just Say No. Don't do it. White House reporters aren't in a particularly good position to learn important things that aren't otherwise reported, and so I'm not really very happy to see someone who I think is a talented and interesting voice move to a position in which he'll be obliged to follow a lot of stuff that everyone else reports on and which, in many cases, has to be reported but just isn't very important.
Yes, we need someone to tell us what the president will do next week (even though, you know, we'll know he's doing it when he actually does it). We need someone to tell us which White House aids are more or less important. We need someone to ask the questions to get the administration on record about things and to pass along signals the White House wants to send -- those are very important functions in a democracy. It just doesn't take, as far as I can tell, all that much skill (and, no, forget the idea that if only the WH press corps was a bit more clever they could trip up Robert Gibbs or Ari Fleischer or Dee Dee Myers or whoever -- that's a nice armchair fantasy, but these people are professionals, and even a third-rate press secretary knows how to deflect a question she doesn't want to answer). I understand that these are highly regarded positions within the Washington media food chain, but it's no accident that the reporters who became famous for Watergate were not part of the White House press corps.
So, I could say some trite stuff about keeping a focus on things that have long-term importance, and avoiding hype in favor of substance, and other things in that line of thinking, but really, I don't think there's all that much point. I guess I would stick to this: don't try to be a good White House reporter; try to be as good a policy and politics reporter as possible, and treat your beat as an unavoidable inconvenience. If your bosses will let you get away with that, it's about the best you can make of the situation.