Relax your mind. Try a form of yoga or meditation, perhaps you could exercise, do something you enjoy to clear your mind of anxiety. After all, you will need a relaxed mind if you want to use it.
Focus on what it is you want to accomplish. Whether it is an upcoming exam, or a tough job interview, you must have your goal in mind. Once you know what it is you want to do, plan ways you can achieve it.
Test these plans. If they don't work, you can always go back to the drawing board! If they don't work, look for a point in your plan that you could have been rethought. It is important to always test plans before the final draft to see if they can be improved.
Attempt the feat that you were aiming for, if you fail, don't be discouraged.There will almost always be another chance. Remember to be confident and prepared for the task.