It can be easier said than done.
When I transfered to University to finish my degree, I just found clubs of interests and threw myself at "whatever" and maintained enthusiasm in myself and others in the clubs. Long story short, I was elected into Student Body Senate after being on campus a year. Demonstrating an aura of leadership can go a long ways.
If that is too ambitious, I would suggest event coordinating. It doesn't require the election process or as much membership/time equity and it demonstrates leading a team to a solution or cause. My last tip would be making sure it is a cause you believe in or a cause that you think will bring positive change YOU want in the organization. Ex: I actually ran a care package drive for my friend who was killed in Iraq with our formal high school. Your motivational statement will write itself if you take that route.