Quickly read through the entire exam paper

Quickly read through the entire exam paper, go back, do the easy questions first, then the hard ones.
The first thing I recommend you do when you are allowed to start, is to quickly read through the entire exam paper. Scan it quickly, looking at the questions to see what will be required to pass this exam. Once you have an overview of what you are dealing with, start with the easy questions first. This will help calm you and give you some confidence. Allow your subconscious to work on the harder questions while you are doing the easier ones. By the time you get to the harder questions your subconscious mind will have come up with some ideas and answers.
Plus some of the easy questions and answers may have triggered info for the harder questions.