Secondly, I believe that writing down everything you need to remember is the best way.
You can do this in the “reminders” app or on paper. If you have a planner or a bullet journal, I highly recommend to pre-plan as a “future log” or any similar action, so you can incorporate this method with the way you plan/journal.
Have a short review session of things you've learned at night right before heading to bed. Giving fresh information to your brain will help store it better while you're sleeping.
Always be curious of what you're learning and willing to understand it first before trying to memorise it. Some things are bothering you? Don't spend too much time trying to grasp it but just the action of trying and looking for deeper information/explanation can go a long way.
If you notice something's hard to memorise or you keep forgetting about it, try to associate it with an idea, name, object, situation or whatever else you easily remember. It may be easier for your brain to associate the difficult stuff to the new associated thing than to memorise it straight.
Also be as aware as possible when learning something that you find difficult: when possible, mix in hearing, writing, saying, doing or watching the stuff you're trying to memorise, or related stuff. That way, your brain will make more connections with that thing you're learning, so you'll retrieve the information more easily.
It's normal to forget stuff. The best way to memorise something is to forget about it because then you have to come back to it, review it, and it really is a normal thing to do.
Lastly, try to have fun and be looking forward to your study /review sessions! Mood affects your learning time quality.