Depends on the style of the exam. If it's written eg four questions, all long answer, subtract 30mins from the time and divide the rest between the questions. Make sure you allow yourself enough time not just to do the questions but also check it.
Take the right equipment with you. If all you need is a pen, take two or three in case one runs out. If you're using a calculator, check whether there are any restrictions, and stick some fresh batteries in.
Make a plan of how you're gonna answer the question(s) and use it to guide you and form a good layout.