Sam- if you're going for a film that you're involved with, you should find out when it's screening and go then. otherwise, i recommend you go towards the beginning, as it's a pretty intense atmosphere, and i think people get kinda burned out towards the end.
that last part is speculation tho. the two times i've been i went for the first few days and was pretty burnt by the time i left. also, i went last year, and it was hard to get tickets to anything good, so try to get them ahead of time if you can.
oh, and bring a HEAVY coat. especially if you're a warm weather wus like us californians.