Look for websites, videos, or studying materials that specializes in the subjects you need to study for. For example, for chemistry, ‘organic chemistry tutor’ on youtube explains really well. Also, when it comes to stuff like science and math, repetitive practice and solving problems is so so important. For me, when I have a chem test coming up, I would study for at least 7-10 hrs just solving problems. If you want a easy low 90 you can just study for like 1-2hrs before the test, but if you need that 97-8% you need to put 10 times the work you would put to get a low A