As a mentor, it is important for you to show the students what to do. Not tell them what to do, but show them, if it is appropriate. For example, if you see a team around you has a really good bot, get your team to go and learn how and why they did it. As for the competition, you are basically in the pits most of the time, and then you go out for a match, and then come back. It's sorta like FRC, but you probably won't be spending lots of time repairing a broken robot, though you may spend a lot of time fixing code and making things run better. At the same time, you must remember that there will be judges coming around, who will ask about their robot, how they did it, why, etc. Make sure the students know what to say, and what not to say. I've had the incident before where I was showing my students how to use Lego Digital Designer (A lego CAD software). They designed it, and since they weren't very good at LDD, I was the one who made what they designed on the computer (just for the picture). When competition time rolls around, the judges asked who made the robot. And all of the students pointed to me and said, "Our mentor did. He designed it on the computer!". They were all happy, and thought I should take the credit for their awesome robot. I had to explain to the judge, who luckily knew me, what I had done.

Well, now that I've typed too much, I guess I'll have to summarize it.

FLL comps are like a low level FRC.

That's a lot better than reading that whole big chunk of text, now isn't it.