Step 1: Review What Others Have Said About the Exam
You can read what other people have said about their experience with the NASM exam here and here. This is the best place to see the latest comments and discussions. The general consensus is that you should know how to apply the OPT model. They will show you an OPT chart with missing information and you must be able to fill in the blanks. You won't pass without knowing the OPT model thoroughly.