I first stumbled across the concept of warming up and cooling down in the book The Mental Game of Poker by Jared Tendler. Having a solid routine will help you tilt less and have more emotional control at the tables ultimately helping you make better decisions
Before every session you should have a warm up and after a cool down routine. You might not know it but you already have a routine. Some typical warm ups are shower, eat breakfast, then drive to casino. Some other are just wake up get online and grind in your boxers, this use to be me when I first started. Other warm ups may be roll out of bed brush teeth go to & casino play. It’s imperative to have a proper warm up. Professional athletes all have warm ups before they play. They review there strategy stretch there muscles. Many poker players do nothing and are upset when they don’t play there best. Jarod Tendler talks about this in detail in his books.
My warm up includes the following. I review my previous days session for 5 mins. I either watch 15 -30 mins of a podcast and training session, sometimes both. I always review my poker goals. Depending on my level of stress or anxiety I sometimes do breathing exercises and or meditate no more then 5 minutes. I sometimes listen to poker affirmation statements that I have prerecorded. I always eat something before playing and pack my book bag with water and snacks. Their are no hard rules in my opinion you should do what works best for you and switch it up.