I need help with school

I am in 8th grade not a grade to be worried about as most people think but I am worried... I am not average student... I don't study n only study one day before the exam and somehow manage to get good scores, I know I would be much more capable if I did study but my brain doesn't agree with me.. I have have exams near and I want to make a difference this year by actually scoring very high... there is this thing about me thinking to get full marks without effort... I sound crazy but if anybody has any idea about this situation a person who was in my own shoes and now is excelling in life please guide me... Please I am desperate...