The best way to remember math is understanding it. There is no other easier way to do it. You can understand the principles of math creating real situations in your life where the presence of math is a must. For instance, calculating the exact area of walls within your room that you want to paint, you'll know exactly how much gallons of paint you need. If you won't calculate the area you can get in one of these two situation: the paint is not enough and you'll have to go back to the store to buy some more or, the worst case, you've spent a lot of money on extra amount of paint you don't need it anymore.
Anyway, the more you create situations that involve the use of math in real life, the more you'll understand better.
Much of Mah is sequential which means that you have to master earlier concepts in order to understand and perform with later concepts.
Depending on what you are taking, you might have to memorize some formulas, equations and definitions. The trend in standardized testing is to give students formulas and equations that they might need to use on a test.
The best way to prepare during the year is to always practice what you have learned over and over again even though a teacher did not assign you to do so. Professional athletes with years of experience are constantly doing the same skill drills for skills that they have proven that they can do in competition. They do this to keep their skills sharp and to be able to perform what they need to do more automatically. Do this in Math and you have prepared all year for the tests that you have to take!