and also never study without sleeping (brain needs the sleep time)
for remembering ? every individual has different ways
what i do is remember random stuff (train your mind the same way you do with the body)
If you have to memorize things you dislike or are hard to remember put some short lists in your house all over the place.
I had once a list of amino acids on my bathroom's mirror.
Around your desk, write with colours, highlight words and stick them to see them always.
And study with music. Not a relaxation music but a brain motivator one. Me for eg i listen Tchaikovski's Swan lake, i have a fav video with an awesome conductor of the orchestra
Maybe for you works kpop (random eg)
If you cant study then first you start with setting goals of what you want to complete in each study session. Add breaks between each study session to make sure you stay motivated after each session. Breaks should only be about 30 min long(max) and you should keep constant with each, dont make one break longer or shorter then the others.
If you dont know how to: look through notes you had and review the content. If you dont have notes look at old hw and review that. If thats not working then review classwork or review the textbook on the chapter your test is gonna be.
Im pretty sure this advice was worthless lol. Hope it helped though.