This is the toughest question to answer and I think there cannot be direct answer to this question. It varies for individual to individual and from time to time. But for sure following rules apply
1 - Regular studies gives better results
2 - Follow a time table
3 - Have good gaps in between for recreation/sports
4 - Try puzzles, quizzes to sharpen your brain
5 - Test your self regularly to see where you stand and plan accordingly.