One thing that I cherish myself is I ask myself after learning a new topic or subject for a class is: Do I really understand everything that is going on?
If you don't understand everything going on you might struggle mightily with an application of the topic or further work in the course relying heavily on that specific topic.
If you don't think you understand it well then go ahead and write down what questions you have about the specific topic and seek answers. Whether it be MSE, your textbook, or your professors, you are likely to find the answers to those questions $somewhere$.
Not only will this help you in your current studies, it will help further your cementation of mathematics in your mind, which is always good because mathematics is a field that builds upon itself in many ways. (For example, If you struggle doing arithmetic, you are likely to struggle in courses that use it heavily.)