(went through this experience myself - sorta)
See if the school already has an existing tech-oriented club, a robotics, engineering, electronics, computer, whatever club that can be "converted" into a robotics team. (We already had a robotics club that did BotBall when i asked to start a FIRST team.)
once you've got a target group of students, go to their meetings, talk to the leaders, and see if they'll let you make a little FIRST sales pitch. doesnt' need to be dramataic. Show them the game animation for this year, and explain to them the spirit of FIRST. Trust me, they'll listen
our robotics team actually more or less ignored the FIRST thing and went on it's previous course of preparing for BotBall until I met up with Patrick and the rest of MVRT at the Cal Games, and invited them over to give a little talk. I'm assuming you probably won't need to do this cause you're already a FIRST veteran and know what you're talking about. but after they came and talked, everyone was just REALLY PSYCHED, and started to go to WRRF meetings, etc.
so basically (in my experience,) it was a.) grab the students, b.) get a mentor/regional forum, c.) register
We really didn't bother with the administrative details because there was already a foundation for a team there, and all we had to do was get interested and register.
if you don't already have a team, ignore everything above