Regularly plan time to relax and get it together. This time may range in units of 10 minutes to whole days according to your needs. You've earned this time off. Exercise is essential for superior academic performance. Your brain would not function well if your body is tired.
Stress reduces performance.
Something almost always comes up to derail your efforts. Allow for it. Floating tasks can be done anywhere, anytime. Carry around a book that you need to read, some cards to review, a letter that you need to write. Self-sacrifice and denial are necessary during midterms and finals weeks.