The BJCP website has great resources- so make sure to use them! You can get a list of judges, flight sheets, score sheets, etc, plus tips on how to organize.
Make sure you have a good list of supplies needed (cups, pencils, crackers or bread, water), and don't make the sessions too long. Give the judges and stewards lunch.
Make sure you have a good place to label and store the entries as they come in.
We've always had ribbons for winners of categories, as well as prizes donated by places like Wyeast. Wyeast has a sign up on their website to ask for swag for donations for these type of events, and I know I got stuff from Brewcraft and Briess. People love prizes, even if they are just bottle openers.
You can combine categories for the purposes of places and prizes, because some categories get very few entries (light lagers) while others get tons of entries (IPA). You still judge/score individually, but you can combine, say, categories 1-6 if you get few entries in them.
Make sure your flights are set up lightest to most flavorful, to reduce palate fatigue for the judges. If you have experienced judges around that can help you with the setting up of the flights, that's helpful.