Thus, to get the most benefit you would want to spend an hour on, let's say, Math. Then spend an hour on History. Then spend an hour on English. However, moving from one subject to another that is closely related to it doesn't help, so you don't want to spend an hour on Calculus then move to Analytical Geometry. They both use the same area of the brain, and you will not benefit as much as if you put a couple of hours between them.
Nothing beats a good night's sleep.
No matter how hard you study, if you are groggy come test time, you won't do very well. The best thing you can do for yourself is to get a full night's sleep before exams. So is a finals grade that averages about one letter grade lower than those of rested students. Spend your study time wisely, and leave yourself enough time to sleep. You will do better.