I play a low-stakes SNG (Sit and Go) for a warm-up, even make some stupid bluffs just to "get it out of my system", meditate, prepare snacks and water, relax... it's like a similar thing you do before the sport even, and an interview - mentally preparedness is as important as any other preparedness, especially in poker. I even write few strategies tips for early, mid, and late tournaments stages (some reminders I post - its a marathon, not a sprint, check your stats every hour on the hour (during breaks), takes notes on players , don't overbluff, pick your "hits and run" etc...