The Study Method
The two types of courses are knowledge courses and Math related courses.
For courses that are heavy on memorizing knowledge:
Use the memory palace or Method of Loci, to commit new information to memory faster and reduce the repetition needed to remember it. To understand concepts faster, try to relate it to everyday things and try to teach it. To review everything you learn and only study what you have forgotten, use flashcard apps that have the forgetting curve algorithm built in, like Anki.
1) The memory palace method, of Method of Loci, is a fantastic way to store hundreds of pieces of information. Joshua Foer's book Moonwalking with Einstein is a good book to read on how to utilize a memory palace. The general principle is to have a layout of place you know well (like your home) and put information in different places.
The reason why it works so well is that our brain is built to remember spatial memory (memory for orientation and environment). For example when you walked into your high school or college the first time you probably had no clue where stuff was. But after a few days it was second nature. There wasn't really a time where you had to sit down and study the entire campus for hours to nail down where everything was. Your brain just memorized it without too much effort. Even after years without going to a place you could probably still remember the layout of the place.
So using this method you can not only remember the information but recall it at will. If you need the name of something, you can simply walk down your memory palace and find the name without any external cues. This comes in handy when having to answer free response questions where there are no multiple choice answers to jog your memory.
To actually memorize a piece of information, take the name of the concept and try to make an image out of it. For example, in General Chemistry 2, we learned about Van der Waals Interactions so to remember that I would place it at the front of the Science building at my college and imagine a Van hitting a Wall. Then out of the back molecules would fall out reminding me that it is the force between molecules.
Even though initially it will take more time to brainstorm the images, the amount of repetition needed to remember information will sharply decrease. Instead of rereading a definition 12 times to make it stick, this will reduce that to once or twice. You could do this without laying the images in a order, but putting them in a memory palace really cements the knowledge and gives you the ability to instantly recall any definition at will.
2) The memory palace is good for remembering definitions and facts but understanding a concept is different than just remembering a name. To understand concepts try to find at least 10 metaphors for that concept. Try to relate it to things you see in real life.
Try to teach the concept, for example, try explaining it to your friends and seeing if they understand. If you can teach it, you mostly likely understand it. I make Youtube videos for concepts I don't understand because trying to teach it to someone else always reveals the gaps in your knowledge. Then I go back and once I can fully complete a video I understand it.
Also, always ask questions. If you think you understand it try to see what else could happen. Taking an example from chemistry again, we understand that raising the temperature will cause water to boil. But what happens if you decrease the pressure? It will cause the water to boil at a lower temperature. That's what you should think about for concepts. If I change variable X what happens to Y. When you ask these questions you will realize that even though you thought that you understood a concept you actually didn't.
3) Flashcards are good for reviewing your memory palace. Use smartphone flashcard apps such as Anki, which are built in with the forgetting curve algorithm. Why I suggest flashcards is due to the fact that they can be studied anywhere. A common complaint is that we lack the time to study in large blocks so this solves that problem. Throughout the day, there are plenty of moments that we are not being productive; waiting for class to start, waiting in line for food...etc. These small pockets of time can be used to study just with your phone which is accessible at nearly all times and convenient. All these small times can add up to 2 hours of studying or more when you thought you had none. Also since it's built in with the forgetting curve, your only studying what you have forgotten so you're maximizing efficiency.
For courses that are Math related:
Do hundreds of problems. Do every problem in your book and be able to explain every single one. When we practice, we don't only do it to get better; we do it to also see the potential mistakes we could make. Every mistake you do while you practice is one less mistake you'll make on the test. Even if you understand the concept of something in the class, it takes practice to see mistake you made on a test. Even if you understand something, there's always a situation that you makes you implement that concept in a way you hadn't thought about, which is not what you want to encounter on an exam. Every time you make a mistake, record the type of mistake and reread that list before an exam so you'll see all the potential places you could make an error.