Some Suggestions and Recommendations:
There is no substitute for thinking clearly on your feet, with a fresh and alert mind.
Experience should help you make reasonable moves automatically, saving your concentration for the close decisions.
Think of several alternatives before choosing an action. The most immediate idea is not always best.
Let your plays speak for themselves; they don't have to be explained to anyone. Especially do not volunteer an explanation that nobody asked for.
When there is only one choice, take it, but also consider a line that holds your probable losses to a minimum. Sometimes accepting a small defeat is much more valuable than staking all on a miracle. Figure out what the opponents can make, and hold your losses to be surely less than that.
In a disaster, get it over with and move on. Prolonging the agony will not help.
"What if" discussions after a bad result (or even after a good result) usually waste more energy than they help. Stay fresh for the next problem. When someone has a disaster, just write down the score quietly and move on.
Take breaks between rounds. Real breaks. Talk about something else.
Fresh and relaxed beats tense and nervous.
Do not let emotion keep you from doing your best. But have enough emotional engagement to enjoy what you're doing.
Do the best you can with what you're given to work with. Do not focus on the things you do not have.
Do not let anything break your concentration. Little things will get an edge into your mind, and there will go your game.
When you are the dummy and out of the play, relax and really rest. Save your mind for the times when it will matter.
Collect as much information as you can before committing to the most difficult decisions. Often the decision can become a sure thing given enough context.
Know more than you say.
Play steadily and don't give away anything in your manner.
Do your thinking before any crisis comes up, so you can handle it calmly.
Do not try to solve the crisis after it has already passed.
