1. Prepare your Clubs & Bag the night before you play - check you have everything you need to perform at your best - Golf Balls, Tees , Spare Gloves , Umbrella , Waterproofs etc.
also check you have correct number of clubs in the bag - even some tour players have been caught out taking too many clubs onto the course.. remember Ian Woosnam at the Open??
Preparing everything in advance you can relax more & leave yourself less to do before you play.
2. Allow plenty of time to get to the course , remember you want to be relaxed to play your best.
On the way to the course it is useful to think a little about the key holes you are going to play & put in mind a clear decision as to the strategy you are going to employ.
Also I have found it useful to review all the positives about playing the game before you get to the course , for me , the people I'm playing with , the scenery & challenge of the game are what makes it fun & addictive - by being thankful for these benefits of the game, in advance means you have already won the first battle - too many golfers base all of their enjoyment on the number on the card - I've noticed if you set out to have fun playing, you usually will & also play well!
3. Warm up before you play - Ideally 30 minutes minimum, short game first , then full swing - with rehearsal on the range of the first few holes - so when you step on the course & are faced with the challenge you've already practiced it , which will give you more confidence when you step on the tee.