Jack Nicklaus once said that he never hit a shot even in practise unless he had a vivid image of the ball flight he wanted to hit and where he wanted it to finish. I have to say that I have done this for many years now also and it certainly helps.
Pre - shot routine
Try 3 imaginary boxes behind the ball.
1. Think box - collect all the vital information required for the shot in hand. Wind, distance, intermediate target and any other critical information you think you need. Culminating in choosing the correct club from the bag.
2. Feel Box - Make a practise swing or two feeling the shot in hand.
3. Play box - Focus on one thing only and play the shot.
Breathing and 1st tee nerves
When you’re nervous your breathing becomes shallow. Breath fully from deep down in your stomach and allow to deflate. Also forget the endless technical thoughts, this will reduce the feeling of anxiety. Practise this anywhere and you’ll be surprised how much influence it has on the first tee.
Make your own course longer in practise.
Try hitting a shorter iron off the tee so as to hit a longer shot into the green. This will make the course seem easier when you return to normal play.
Essential. Don’t attempt to concentrate for the whole duration of the game. Just purely for the 60/120 seconds as you get to your ball and play your shot.
Then in- between relax and enjoy the day, company, scenery and just have fun.