To start with, 1st identify what to prove. Suppose we are considering a geometrical proof, then strategy would be moving in opposite direction of statement to be proved to reach the final statement. Check for proofs that already exist and are suitable to be used for completing your proof. Also note down info given in the problem.
Next we decide the method that has to be followed to explain the proof. We can make one option out of 2 - columnar proof, passage type proof & flow - chart proof. For proper understanding 2 - columnar proof is generally undertaken. In this there will be 2 columns with one having the statements that we write in proofs and other for reasons to specify the purpose of using that statement. This way we can prove that assumed hypothesis is wrong by moving in right direction and hence our initial statement is true.