Easier said than done, we know, but it's important to try and keep level headed throughout the exam. One of the main reasons for stress at exam time is the lack of control. Students get stressed because they don't know what is coming up. One of the best things you can do to calm yourself is to visualize yourself in the exam hall. Reading the paper and picking out the questions you are going to do early on will help calm you as it removes the stress caused by the unknown of what's coming up.