I am no expert on the perfect test taking skills. But this is what works for me, and I don't end up too stressed, and I do end up with the results I would like. I thought it'd be a good post, especially with AP tests coming next week and finals coming soon.
1. SLEEP. I know a lot of people think that studying late will be more advantageous, but really, you need sleep. I can't stress that enough.
2. Work in a place that won't be distracting, and don't work in your bed. It'll be harder to sleep later, and you'll be more fatigued if you do work in bed. Don't have any temptations like a TV or phone around.
3. Food. It's okay to eat a lot while studying hard. As long as it's healthy, it will give you tons of energy that will help you keep focused. Try to stay away from junk food (except a little sweet now and again :D) Try to drink a lot of water too.
4. You don't need to go over things you absolutely know. I always only look over stuff I know I'm unsure about, especially if it's a lot of material.
5. Taking a break is okay. Don't worry that you need to spend hours studying. I will usually do 30 minute intervals of a break and studying, more or less.
6. Your friends are a great resource. As long as you guys hit the books, it really helps. I would be failing physics without my friend and I studying together for each test.
7. Choose a motto. I like "you know more than you think you do." It helps me de-stress.
Hope this gives a little encouragement. Everybody works differently, so cater your studying to what you need. One more little tip, if you want to scream, scream. As my mom says, it releases endorphins (oh mother). Just remember it's all going to be okay, and good luck!!