Not to be redundant, but GPA and DAT scores should be number one on your priority list right now. Every year it gets more competitive to get into dental school- I think that trend is only going to continue as more people are seeing that dentistry might be a better gig than medicine.
Try to get to know your professors so they can write you strong letters of rec.
I would use your summers to shadow dentists, do community service, and possibly research. I think a 3.2-3.4 GPA and 18-19's on DAT used to mean that you were in... but not now. The research, community service, etc. can help set you apart.
So in summation: During the school year- work your butt off and get more A's than B's. During the summers, start studying for DAT, and focus on all the "extras" for the application.
Lastly, submit your application June 1!