Surprisingly enough, the first day of Movember is the clean shaven one.
I probably should've mentioned this before now, but the way it works (according to the MOnifesto on www.movember.org) is you begin the MOnth clean shaven (31st Oct), then over the course of the next 32 days you grow whatever you can on your top lip. Nothing in the imMOdiate below-lip area is permitted, and no joining up with sideburns.
So a Derek Smalls / Uncle Chop Chop would be fine, whereas a Frank Zappa would not.
Be sure to shave every couple of days as normal and let the mo develop. There's no pretending you're growing a goatee and then suddenly whipping the bottom bit out to surprise everyone with your mighty lip slug (although that is kinda fun too).
Or you can just play by whatever rules you want really. The Mo's the thing.