Generally the first round of invites are mailed around Labor Day in early September. Interviews are usually conducted in October and November with the first acceptances going out December 1.
I guess my second question is, if I do some community service over the summer, will that help my application in any way? How should I signify to schools that I am doing this work?
There are a handful of schools (ie. Case, Nova) that will send out invites as early as July and start conducting interviews in August. If you are concerned about a specific school go to www.predents.com where you can view the actual interview dates of applicants last cycle.