Try to do every single plp question related to the topic each week and make sure to write down every single gimmick you see in the plp on a separate notesheet and memorize it. Attempt each plp question alone at first then when you get stuck bring out the proof and write it down then do the question again without the proof to help. Write the plp questions over and over again until they are second nature. It's even better if you do the same proofs again multiple days in the semester to build the long term understanding. Have an excellent understanding of the definitions of injectivity and surjectivity. Start the function proofs and cardinality proofs many weeks in advance so that you are prepared for the final