I'm a first time FLL coach this year as well. I'd never even heard of FLL until just a few weeks ago when a mom from our school sent out an email looking for kids to sign up and potential coaches. However, I am a programmer and I've used both the RCX and NXT before, so I should be ok there. The best thing you could do, if you can swing it is to buy yourself an NXT retail set and build the basic robot and start playing with the coding yourself. I realize that's a pretty hefty personal expense, I got lucky and had a birthday a couple weeks ago and that's how I got mine.
The other thing I'd suggest is to look online. I've found a couple good books in pdf format. One is something like "Winning Robot Design with Mindstorms NXT" and the other is a "The Art of Lego Mindstorms NXT-G Programming" Both were PDF's that I found online and even though I wasn't specifically looking for pirate copies, I'm not sure they were meant to be free either. The second book however is probably a good one for you to start with. It's very detailed. I skimmed through a good portion of it vs reading it. If you have a good understanding of the process and the blocks used in NXT-G, this is a good refresher and you will still learn some things.
If all goes well, we're going to be writing our first program next week and I can't wait! Good luck, Coach!