I would organize different positions for some of your members to hold IE Team Manager, Electrical Person, Mechanical Person. Strong leadership definitely helps. All those positions should be elected by the team and have clearly defined responsibilities. Always communicate between each other so you know what's going on between the groups this is crucial in the begining when you are working out a design for your robot.
During the preseason, hold workshops for your team members. Show them the skills they need, to be productive during the season, like wiring, how to put together a pneumatics system, programming etc.
A Team building activity would be fun. We played Counter-Strike one year which actually happens to be a very team oriented game.
If you don't already, sort your members into areas they want to work in. If they're not sure tell them that nothing is permanent and they can move around a bit if they want.