1. Take some time for yourself.
Make sure you're not giving up your "me time". If you're extroverted (you gain energy from being with people), hang out with some good friends or talk on the phone with someone (who won't add to your stress). If you're introverted, like me, and you have to recharge by being alone, take some time to step back from what you're doing and watch some TV or read a book (or some comics)... Take some time and relax. Find something that makes you laugh (laughing makes you healthier, right?).
You could also try these relaxation techniques from the Mayo Clinic. I'm terrible at meditating, so do what works for you.
2. Have a Game Plan
Prioritize which things need to get done when, and when you're going to have time to do them. I procrastinate like crazy, so at 2:00 in the morning when I'm trying to write three different papers I should have started ages ago, I'm really stressed (surprising, right?). Avoid that all together by spacing projects out as much as possible. Easier said than done, I know, but worth it in the end. And, since you have time because you didn't wait until the last minute, you can try the Pomodoro technique so you don't burnt out as fast. You could also check out this list of the top 50 apps for time management.
3. Get help
Professors can be pretty cool people. If you're overbooked and need an extension on something, most of the time it doesn't hurt to ask (as long as you ask reeeaaally nicely and ahead of time).
Because of the way my class schedule is this quarter, I'm supposed to take three finals on the same day. That just wouldn't work out super well, so I'm going to cut myself a break and get one of them moved.
Hope this helps! I'll try to post more tips as I find them.