Part of mental preparation for competition is ensuring that you start your performance in a state of flow. Many high level athletes do this by developing routines that help them to focus their minds and block out distractions. These may involve complex and detailed rituals that involve preparation, detailed dressing rules, or precisely executed warm-ups. Part of this practised routine might involve specific sports psychology skills such as imagery, positive thinking, mood control and distraction and stress management, perhaps using a Training & Performance Diary.
All of this ensures that you enter a competitive situation in the ideal state of mind to give an excellent performance.
Experiment with developing a ritual that covers all points of preparation that you consider to be important. By practicing this ritual and keeping it standard in training, it will be automatic and complete when you face a potentially stressful competition.