One problem students face is remembering what you studied. Understanding your brain and how memories work is the key to improving your memory. Especially in college, I felt that there was more material to be learned than time to learn it! Here's how I trained my brain to retain:
There are a series of steps to improve your memory and focus. When you're first introduced to a concept, whether by reading or listening to a lecture you're creating a memory. You keep this memory in your head, but to reinforce it, you can relate it to something else. For example, you could make up an acronym for a concept, or think about an animal that you'd relate it to. Sometimes, it could be as simple as consciously thinking about the concept and trying to remember it for later.
The next, and most important step is to recall this memory. I found that reviewing my notes the same day after class was very effective. Read the notes, and try to remember what your lecturer said about each topic and concept. If you don't remember, mark it down with your pen or sticky note to ask them later at office hours. The next day, quickly read through your notes once more. In a week, review that material again, this time with more specific examples. This is active recall and the more you try to remember a concept, the easier it will come to you. By spacing out your study time gradually, you improve your memory on that particular topic, and gaining long-term memory!
Researchers also think that exercising can help improve your memory. Your brain simply functions better with exercise and you can benefit from the boost in your mental and physical health as well! Even if you can't work out every time, I recommend at an hour a week of getting your heart rate up. This mainly will boost your spatial memory, which means you'll also remember where you were and the things and people around you. These can help act as "cues" for when you are trying to actively recall your lectures.
Lastly, SLEEP! There's an unhealthy students' tale about somehow being most productive when you're pulling all nighters. This is simply not true, and if you're one of the few who passed their exam doing this, know that it will not always work and you probably would have done better had you managed time effectively and slept. It's been proven that sleep helps your brain retain more information, and some people who stay up later don't realize they're just seeing an illusion of productivity. You may actually be very slow and won't remember what you studied!
So repeat these steps: learn, spaced out active recall, exercise, sleep. By the time of your exams, you'll know your material well and maybe stop forgetting the name of that classmate who always sits next to you.