Back to school is such a stressful time and I can't never live it in a relaxed way. This year I tried different things, surprisingly some of them worked. I would say that the best tip is going to bed early, DO IT! You wake up feeling much happier and it helps you a lot on long exhausting days that seem to never end. It's not the easiest and I love staying up all night watching Grey's Anatomy but hey you have to admit it: summer holidays are gone :(
The second tip is to prepare everything the night before, sometimes you'll need a little lie in.
The third tip is trying to get your homework done on Fridays, you'll see that organizing your work load is worth not going out on a Friday afternoon (if you work hard Saturdays and Sundays will always be fundays).
The fourth tip is to use the notebooks, pencils, highlighters you like the most, I find it useful. You could also listen to some music if you aren't doing anything difficult that requires concentration.
The fifth and last tip is to enjoy school! I'm 14 so I know that the first few weeks can be scary because of your teachers, awkward because of some of your classmates ( we all know that feeling when you see someone after three months of holidays: they don't even say hi, you just look at them feeling embarrassed) but believe me it will be all different after a while! You are not going to school forever, this means you are not going to do P.E. lessons with everyone laughing at you forever, it also means that you are not going to be able to see your friends everyday, that you are not going to have so much fun forever! I think that life is made of "phases", you only live once, ENJOY EVERY SINGLE SECOND OF IT!