I'm the opposite. I can rock exams and hate assignments. Whilst it's an open book exam, don't rely on that. You usually run out of time looking things up. Make sure you know your stuff anyway.

Work out how many topics you need to revise for. What kind of questions are involved? Essays, multiple choice, numerical? How long is the exam and when is it? All these can determine revision techniques.

Break down the curriculum into number of topics. Create a mindmap for each one, using different coloured pens. Not too much detail. Write down main points on flip cards. No more than 5 points per card. Go over them, then shuffle them back and forth. Do practice exams. Set a time and keep to it. Eg, 10min reading, 20 min on multiple choice, 40min on longer questions which may mean 10min each, 60min on essay. Move on when your time is up for each section. You can come back later if you have time.

My best tip: burn rosemary oil whilst revising. Then rub a bit on rosemary oil under your nose as you walk into the exam. Not only does rosemary aid memory, using the olfactory sense is one of the best association techniques.
Every thing above I second! I also find exam easy and it's mainly from the prep work I do before hand. I only did one open book and I made sure I knew where all my notes were - ie a really detailed index. The open book exam focused on skills such as extrapolation and synthesizing data rather than recall and application.

TMI alert: I also always went to the loo before hand to literally 'cr* p myself' which helped me as well.

Breathing slowly also helps as if you start hyperventilating thinking about it, it won't help you during the exam.