This is a great question.
Everyone learns differently and there are multiple ways to learn the same topic.
The first question to ask yourself is how to I absorb or retain new material the best?
Some people are visual learners: they have to see it written down.
Some people are acoustic learners: they have to hear it or repeat it out loud.
Most people are a combination: they have to hear and see it AND write it down.
Figure out which one of these learners you are and then reinforce your learning.
You may need to adjust this for different types of classes because the same method may not work on every class.
Listen to the lecture/class and take notes. Highlight your notes or make flashcards.
Give yourself hints to remember key concepts like taking the first letter of each group of items in order to recall them on a test.
Go to office hours and talk to your teacher or teaching assistant. Figure out together which concepts are difficult and practice these together.
Take practice tests if you can before the actual test or create your own test questions.
Study with a friend.
There are many fabulous tools online like utube, google, and khan academy so you can actually see someone present the material in different ways, learn a topic, and get hints from other teachers/professors.
Keep reinforcing the material by writing it down, making colorful study notes, or posting it around your study area. quiz yourself constantly and try to apply the topic to your real life if you can.
Try some or all of these techniques. Good studying!