After finishing Unit 50, go back and re-do the exercises of Unit 15. You will be surprised how much you forgot. This "spiral" approach locks knowledge into long-term memory.
English Grammar in Use is excellent but can feel chaotic. Oxford Practice Grammar is more structured, with clearer categorization and better for learners who need explicit rules. If you find Murphy overwhelming, switch to Oxford. oxford practice grammar upper intermediate
Passive recognition is useless. After studying a unit, force yourself to use it: After finishing Unit 50, go back and re-do
Read an exercise sentence out loud. Then, close the book and say it again from memory. Then, modify it: change the subject, verb tense, or adjective. This activates active recall. After finishing Unit 50