I co-founded a biology-medical student organization in a community college in the hope of informing the students there about graduate school and possible career options. The first thing we did was actively recruit people (we had to get ~15 signatures of student). Then I drafted the organization's constitution. In the constitution, I wrote about the mission of the club, the various positions of the club (jobs of officers, how to elect officers, how many officers do the organization need, how to impeach officers, etc), and then I wrote about the club's specific goals (planning an event at least once a month, weekly meeting, etc).
After completing the constitution of the club, I submit it to my college's student body. I then had to asked several biology faculty members to be the advisor of the club (this is the hardest part for our club). After the advisors agreed, I then presented my proposal to the student body. The officers of the student body were informed about my club and I had an orientation as a representative of the club. We host our first meeting the next week or so. Election was on our second week.
You can go ahead and use the same "proposal" that I used. Try to get input from your advisors too. Make sure that when you lay out the details of the proposal, stick to your mission. It makes it easier for your proposal to be approved (in my case, at least).
