12 hours a day even during exams sounds like a bad idea, I don't see how anyone could actually absorb that much substantive work in a day. I treated the first semester more like a marathon than a sprint, as I go to a lower T2 and knew top 10% was absolutely critical. This is what helped me pull a 3.7 on a B curve:
1. Read EVERY case and take notes on them - You'd be surprised how many of your colleagues slack and largely ignore the casebook and follow supplements instead. I didn't formally brief every case, but i jotted down enough of the facts and legal reasoning that I could recall how the legal rules applied to the particular fact set of a case. Knowing the black letter cold is certainly necessary, but your application of that law on an exam will be MUCH easier if you can analogize/distinguish your hypo from the facts of the cases you read. This will put you in a FAR better position than your classmates who know nothing about the cases, especially if you have an open book exam. It is critical that you distinguish your exam from your classmates' and I think this is one of the best ways to do it.
2. Work consistently rather than in bouts and spurts - I put in about 4 hours a night of meticulously reading my casebooks, day in and day out. Sometimes it would take me an over an hour to really understand a 10 page case, but after that I knew it pretty solidly. Class time basically served as a second run to solidly the cases/laws/reasoning in my head. Weekends I did about 5 hours of reading every saturday and sunday, and went out both nights. This made for about 45 hours of work every week and helped me avoid the 12 hour a day marathons right before finals.
3. Do most of your work alone, use study groups sparingly, avoid the law school rumor mill, make your own outlines - You will hear all semester about some AMAZING outline that is floating around. However good it is, don't be tempted to completely rely on it. Again, the name of the game is distinguishing yourself from your peers - you can't do this if you all use the same outline. Same applies for using big study groups too often.
4. Have a life! - Even during the 3 weeks before and during finals, I managed to go out one night a week. This was really key for me in terms of keeping my sanity and blowing off steam. I think it definitely helped me absorb the reading I did when I went back to the books. Whatever you love to do with your free time, make sure you find time to do it - It will make the hours in the library far more doable.
5. Get rid of as many other commitments in your life as possible - 45 hours a week of reading and class is pretty reasonable if you don't have an hour commute, part time job, annoying girlfriend, family obligations, etc. I came to law school right out of undergrad and was considering waiting a year or two, but realized that the older I got the more likely it was I would have more going on in my life that would inhibit my studies. Obviously, this isn't possible for many people, but if you're going to go to law school it should be your absolute number 1 commitment. Being able to boil down your whole existence to law school work and having fun will help you avoid feeling burnt out, even during finals.