There is lots to learn in jiu-jitsu. You will forget more than you remember. This is okay because your goal is to absorb what is useful and discard what is not. But how can you improve your memory of what is useful to you?
Relevance. When you roll and are able to successfully apply what you just learnt in class, then what you learnt is relevant and you should endeavour to remember it.
If you can’t apply something even when it is fresh in your mind then it is just useless knowledge with no practical use.
Resistance. While rolling, you recognise a situation you are in and then recall previous times you were in this situation. The closer your practice was to the rolling situation, the easier it will be to recall and remember what to do.
When you don’t practise with resistance, the rolling situation is too different to the practice situation and recall will be slower.
Repetition. Repeating something reinforces it and makes it easier to remember. But each repetition is not equal. Repetition should be spaced. 10 reps a session for 5 sessions is much more effective for retention than 50 reps in one session.