Good daily study habits will increase your confidence. Never skim an exam. Do not look ahead at the questions that are coming. Skimming only reduces your confidence and concentration. Any answer given on the basis of quick reading will probably be wrong.
Relaxed concentration is the key to effective exam-taking.
When you start answering the questions, just concentrate on question 1. Forget question 2, forget your grade, forget your argument with your roommate. Then think over every one of the 5 possible answers. Take them all seriously, until you have finished all 5. Don't jump to conclusions.