Rusty,
You're probably looking for a lengthy answer, which I don't have time to provide right now, but I can make a couple of comments.
Regarding letters of recommendation (LORs). See what your school offers. If your undergrad offers a "committee letter," like mine did, then that may be the way to go. A committee letter is compiled by somebody at your undergrad institution interviewing you AND reviewing the actual LORs you have received (typically 3). The committee member then summarizes your applicant status (essentially writes their own LOR based on your interview with them AND their reading of the other LORs) in their own letter. This letter, along with your original LORs is mailed to AADSAS and then forwarded to the schools.
Either way, you SHOULD start thinking about LORs right now. When I applied, I had my authors turn their LORs in by mid-April. That gave them plenty of time to get them done, and also gave me a little lead-way if they didn't finish them on time. Remember that often the people you ask to write your LORs are also asked by many other applicants for LORs. I knew that I wanted to apply to AADSAS on the first day it was available (end of May/June 1), so I based my timeline around that goal. Your goal for application may differ, however getting your LORs out of the way is a good thing, because they can often be the link that slows down your application.
You don't have to join any clubs or organizations, and by all means, if those things don't interest you then don't do it. Admissions committees can usually sense when somebody has joined an organization just to list it on their application. What I WOULD recommend is that you do some things that interest you. If you like sports, then volunteer to coach for elementary kids. If you like research, then do research on campus. You can tutor, hand out food at food banks, volunteer at hospitals, do community service--the list is endless but it should be geared around things you truly feel passionate about and enjoy contributing to.
You can get some better answers from the AADSAS website. The information listed there is still for the 2004 cycle, but it won't change between now and the 2005 cycle:
http://www.adea.org/AADSAS/default.htm
Good luck.
