Well first of all, know the different types like contrapositive, contradiction, induction, converse, irrationality, negation, etc. Honestly, proofs is just like any other 4U topic (calculus, motion, complex, etc); just practice heaps, get used to Question 15/16 regarding proofs (if this is your weaker area). Honestly, your best resource is just past papers (if you want them sorted by topic, HSCNinja has that sorted for you)
Would recommend downloading this link -->
https://educationstandards.nsw.edu....-6fd6e50d-773e-4129-b9ca-6c939bb2a5b8-ndljHTs