Harry potter and the HBP midnight premiere showing?

ok so im going to the midnight premiere for harry potter and the half blood prince(YEEEE!!) and im wondering what time i should get to the theater to get good seats. i already got my ticket from fandango so i can "skip the box office and go straight to the ticket taker" but im still wondering how crowded it usually is and how much earlier i should be there so i get a decent seat and everything. and for anyone whos previously been to one of the midnight premieres is there anything i should know or expect? thanks!