Some random thoughts:
1. There is NOTHING you can do the summer before starting to make it easier other than relax and have fun.
2. You should buy a medical dictionary (not JUST a pocket one, but a big one as well -- I like Stedman's) early.
3. Keep active. It's easy to get bogged down.
4. Keep perspective. When you're studying crap all the time, you lose it. Get a preceptor and take a history from a patient, and remind yourself why it is that you have to learn about fatty acid oxidation or whatever.
5. Make a friend in the M-2 class. Better yet, make a few. We med students, now that we're here, are quite a noncompetitive group, and love to share our knowledge of easy professors, tips on difficulties, etc...
6. Realize that you'll pass, and most likely, you won't shine (the majority of us, anyway!) What does this mean? NOTHING! You'll still get a good residency, and live happily ever after if you don't remember what the hell APE CLAW has to do with your future livelihood.
Just some thoughts...
Enjoy your summer -- MOST IMPORTANT!