If there is one organizing principle to my philosophy of life / human psychology, it is this: you do what you want to do, in every situation in which you have any control over your actions.
If you think this is trivial, it's probably because you think this just comes down to the definition of "want"; I didn't say this principle explained anything, I just said it organizes things. If you think it's wrong, it's probably because you think a sense of responsibility, or morality, often guides you to act against your desires. If you grant free will, however, you act "morally" because you want to; it's not externally imposed, you choose it. Trivialization? See the beginning of the paragraph. I think of this principle as a restatement / generalization of a principle of "rational self-interest" that allows for second (and higher) order causes for action (like love, moral codes, etc.)*
I'm thinking about settling on a second principle, not unrelated. I don't have as succinct a way of phrasing it, but I think it may be just as solid and important. If you have no "wants" at all, you will try to find or create them; human psychology abhores a vacuum in the space of desire: this is at the root of "meaning".
You don't worry much about meaning when you're starving, or calling a girl to ask for a date, or rushing to meet a deadline. You worry about it when you're idle, when you don't care about your work; in general, when you're satiated. I think this is more than a coincidence, more than a deep concern surfacing only when not obscured by the immediate. I think in a very general way we have a "meta-desire" to desire, and it is only the absence of immediate desire that leads us to seek external motivations for desire, which we identify as "meaning". I guess I'm not totally sure, though, so I welcome debate.
* and leaves out any moral "assignment" like that of Ayn Rand style "objectivists"; there's no "should" in an organizing principle; it's just stated for the sake of understanding. posted by Miles 2:11 PM