To really learn a new subject or concept, you often have to master the facts of the subject as well. (And you often have to show that you know those facts on a test.) One technique for improving your memory is association, where you create a vivid imaginative relationship between something you already know and something you want to remember. Here's a really simple example:
You want to remember the definition of a "prime number," a number that has only itself and 1 as factors. You could simply associate something you already know about "prime" with the mathematical concept. You could use the well-known cut of meat prime rib. One could say that prime rib stands by itself. There's no other variety of beef that tastes as good as prime rib, assuming you're a carnivore. Just like prime rib, prime numbers stand by themselves alongside of the numeral 1, of course. This might be a poor association memory trick for a vegetarian; the point is to use your own imagination to create an association that works for you.