be active in class. go to your classes and ask your teacher when you don't understand something. your teacher will most likely explain the things that they think are important, thus the things that will most likely be in the test
get atleast 6 hours of sleep, your brain needs some time to rest to be able to focus
stay hydrated and take some snacks with you. i don't know all of you, but i can't concentrate well when i'm hungry or thirsty
discipline. don't procrastinate, i know it's hard, as i also have problems with this one. but when you study on time it will be more relaxing and your brain gets more time to process the information
make notes during class, as i mentioned before, your teacher will explain what they think is important.
DON'T study 24/7. you need some time for yourself to be able to enjoy going to school and to study! don't make yourself stress out about school all the time, do something besides studying that makes you happy and you'll go to school happier for sure
watch online videos about the subject. if i really don't get something even after asking, i try to find my way online and most of the time it actually works!
keep your notes neat. if you're notes are super messy most of the time you'll find it hard to find the things you're looking for
+ these are some tips that work for me, so they might not work for you