Certainly between games you need to chill...and eat something that will last long. Avoid candy bars.
Just as there are sadists, masochists, alcoholics and drug addicts, there are people who love the tension, nervousness and butterflys that come with competition at the highest level. Each person has to discover how he reacts to the pressure. The great golfer Walter Hagen once had a playoff for the US Open the next day when a reporter found him partying with some beautiful women in the wee hours of the morning. The reporter asked if Hagen was worried that his opponent was in bed alsleep. Hagen replied "He may be in bed, but he's not asleep." Hagen won easily.
Inhale slowly, starting with the diaphragm, and slowly filling the lungs from the bottom up until you can feel the slight lift in your upper chest or shoulders when they fill up. Then even more slowly exhale in the reverse order, continuing until you expel ALL the air, then inhale again.
Roughly you should inhale to a count of 7 and exhale to an 11 count.
Practice it, and do it 10-20 times before each round, and during the game when you begin to feel nervous.
Have sex, go to the beach, smoke a big spliff, and enjoy a real good meal (not to big). Do all these in no particular order, but you must do all four, and you will be relaxed. I guarantee it.
Hmm. He's 13 though.
Good point - he'll need a ride to the beach.
Meditation, a nap, and a vigorous walk always help me.
I find laughter is a great relaxer. Watching a funny movie or reading jokes gets my mind off the worries. Also exercise is good, deep breathing is good.
What I do is,My rating is 1577.Suppose i get an opponent rated higher than me,say 1800.I think,1800?I really wanted to play a 2000.Let's beat this guy fast and get it over with so that i get a higher rated player soon.If i lose I just think,huh.He wasn't too bad.When I get lower rated players I just act all confident so that my opponents get intimidated by my rating.You lose all your nervousness by applyin this.
You need to be focused, sharp. It's the state in between totally relaxed and too nervous. Neither bored nor overwhelmed.
Before the game, try to find out what your current state is, and beforehand make some plans for how you'll raise your alertness if you're not fired up, and how you'll calm yourself if you are too tense.
Meditation, breathing, soothing music, a quiet walk, that sort of thing is good to calm down before a game.
If you aren't excited enough, do something that pumps your adrenalin, whatever works for you. Troll a bit on chess.com, run a sprint, listen to Rage Against the Machine, hit a team member, kiss a team member, try to do both in various orders, steal an opening book at the book stand, what have you.
To answer the OP's question: I have a routine. Breakfast and coffee, shower, drive to the venue listening to old crooners and show tunes, point my Knights in the right direction, take score with my lucky pen.