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Make sure you have all the required books, materials, etc. Sit down in a quiet space and set targets of how much you want to accomplish in what duration of time. For example: In 1 hour get 5 pages done. Take short breaks and get back to studying.
I like to go through the material and write up an outline on everything you need to study. Not necessary to write word-for-word definitions, just what you need to understand the definition for example. Then write a quiz for yourself, and take the quiz a few hours or more later. Then focus on the things you missed in the quiz, and repeat the process.
Its also helpful to say things out loud as you study, or to try to explain an answer to someone else. This can help you remember the information in multiple ways (like muscle memory, physical location on the outline, the sequence of words, the concept, etc). Even writing in different colors can help you remember the information.
For math classes, or classes with equations, I write up a list of all equations, and then come back and quiz myself in what situation I would use the equation, or what key words to look for.
Hope this helps.