Reddit reviews The Manual: A Guide to the Ultimate Study Method (Concentration, Super Memory, Speed Reading, Note-Taking, USM, & Rapid Mental Arithmetic), Second Edition

Two things will greatly help improve your memory:

1. Practicing mindfulness.
   
2. Practicing mnemonic (memory) visualization techniques.
   
   For the first, I highly recommend the book The Mind Illuminated by Culadasa (and the accompanying subreddit r/TheMindIlluminated). Practicing meditation in this way will develop extremely powerful mindfulness, allowing you to be very aware of what is happening in your experience at any given time. As a side-benefit, you also get enlightened, so that's nifty. :D
   
   For the second, there are dozens of books on memory techniques. My favorite is The Manual. I haven't practiced it much, but to give you an idea, a basic memory trick beginners can learn is to memorize an entire deck of cards in order. These techniques are amazing for studying in school, especially for things like biology or language where there is a ton of memorization involved.
   
   Also if you smoke a lot of marijuana, that will also not do you any favors. Reducing your consumption will help your memory a lot, as one of the effects of pot is loss of short-term memory, and what doesn't enter your short-term memory has no chance of entering your long-term memory.
   
   There are also a number of supplements ("nootropics") that help with memory, the choline family especially (look up CDP Choline and Alpha GPC and experiment for yourself).

Tim Ferriss has a lot of material on the subject. And this: https://www.amazon.com/dp/B019LT9I6M/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1