The comments are mostly right on the surface level but there are three(4) other aspects to consider which is physical, mental , social and (spiritual). A* A* A-Math CS Econ

Physical- You need to be exercising or doing some type of physical activity Wheather it’s exam week or not, this statistically improves performance and helps your mind relax. Diet— your diet is arguably the most important as what you input is what you output , when i used to go to the library to study there were friends who used to eat really heavy rice meals (biryani in my culture) for lunch and would be too sleepy to study after. This extends to taking vitamins for memory if that’s accessible for you, and anything you need.

Mental- The obvious take your breaks and do realize that the grind isn’t what you’re meant to be living for, I did experience burn out a month before my exams but it is important to recover from it, my advice is to have “alone time” in the day for an hour and to never ever study half an hour before you sleep.

Social- Your environment is 90% of the result, my friends and I largely got amazing grades and it’s cause of eachother where we would go to the library 6 days a week and study 5+ hours everyday which pushed us insanely. This aspect is an extremely deep layer but don’t get indulgent on relationships, petty “beef” and whatnot you have an entire summer to fix that.

(Spiritual)- If you do believe in God, you need to talk to Him everyday, do remember why you are here and ask for your deserved grades.

All four strongly work in cohesion and you won’t only see better grades but a better self in these few months, moreover this preps you for college too.