The most important thing, for me at least, is make many exercises about the topic instead just read and see the classes.

Hi Vivian! My study methods vary by class, so I'll give you some general tips about what works for me.

For classes that involve a lot of textbook reading, like history, make sure you read actively; in other words, don't just skim the words and not retain anything. Do something that forces you to pay attention to what you're reading. I like to take notes (which double as a study tool later on!) and ask myself questions about what I just read. Many textbooks have discussion questions already in them, so make sure you can answer those. If you're allowed to mark in your textbook, you can annotate the text by making notes in the margin or highlighting key points.

For classes that require memorizing vocabulary, like science, I like to use flashcards. I personally use the website Quizlet, which is essentially flashcards online. It's free, and you can use a variety of options to study (flashcards, practice tests, matching, etc.). There is also an option for you to set a test date on a certain set of cards, so as your test date approaches, it will send reminders to you to on your phone so you don't forget to study.

For classes that require you to apply what you learn to specific problems, like math and some science courses, do as many practice problems as you can until you are comfortable with the material. You can get practice problems from your textbook or right here on Khan Academy! 

In general, make sure you space out your studying to avoid cramming and burn out. Supplement the materials you get in class with podcasts or videos on YouTube (for example, I use Crash Course videos to help me with AP Biology). And never hesitate to ask your teacher or peers for help!

There are free books on freebooks.net on maths and tones of pdf books on the internet, i struggle with identifying angles apart from the 90 degrees and 180 degree and likes of sin, cos, cots etc equations I am familiar with trigonometry I have done them plus geometry on Khan academy, so now I am reading the pdf books.

I prefer flashcards as my go to study method. I go home and listen to my lecture recordings and build a base set from my lecture notes and any material provided by the professor. 

Than I do the assigned reading while highlighting anything I find interesting. I'll go back and update the flashcards after that with any extra details. Than listen to the lectures once again while at work. 

Finally I challenge my active recall with by drilling until I get through all my notes. Best method I found for retaining information for my exam. Than when the final shows up I go back to all my sets for refreshing.