What we found that works is making people really experiance the thrill of FIRST and telling them about it later. We would bring our robot into our school and just have people drive it around the gym and such. Sometimes I take a few people to competitions to show them how it feels like to be in FIRST.
-I've found it hard to convince people verbally that FIRST is more rewarding than some other activities, but when they actully get to try some of the things they learn FIRST in their own way and they want to stay as long as possible.
-So recap, let students drive your robot, bring students to off-season FIRST events or even Kick-off if you are still introuble right before the season starts, and lastly promote your team like crazy throughout your school. Something I started talking about with the Frogs is just playing those FIRST videos that they play to start every Season event. I think if we play those during school we can turn some heads
.
Good luck! Oh, and for a team leadership role. When someones a leader you will know it. And just remeber that the leader of the team does not have to be experienced in Robotics. The leader is someone who can push the team in the right direction and be a good spokesman to other teams.