I asked the same question before entering dental school. I had off from December till July and didn't know what to do besides work 3 days a week. I heard the same answers that you're hearing and (not to take anything away from what they are saying) but it didn't satisfy me.
With that said, here are my honest answers:
1. Get in shape.
This will do wonders for you. It will get you into a good rhythm of exercise, get you eating right and NOW is the best time to do it. Never will you have a better opportunity. Look your best before entering dental school... ha, i know several people in my class have put on a few pounds already.
2. Learn BASIC dental terms.
I'm sure that now you have been accepted to dental school a bunch of people have asked you questions about their teeth and whats wrong with them. I'm not saying learn all the pathologies associated w/ teeth i'm saying learn dental vocabulary (especially as to what pertains to Dental Anatomy.) Learn what mesial, distal, buccal, labial, lingual, incisal, occlusal, gingival, apical etc means and be familiar with them. Of course you will learn this in dental anatomy but this is just something simple that will help you out a lot.
3. Review basic gross anatomy
i'm not saying to go into great detail...but look over the skeletal system, the muscles, and various organs.
4. work with your hands
if you haven't already...pick up a hobby that requires attention to detail and fine movements.