To date the best practice regiment I have ever heard was that of Stephen Hendry years ago. He would set his alarm and wake up at 7 am every day Monday to Friday. Get showered and dressed in the same attire he competes in. Have breakfast and report to his table at 9 am. He would take a 15 minute break before and after his half hour lunch break. He played till 5 pm everyday. He treated it the way most of us treat OUR jobs. He worked 40 hours a week and never called in sick.
To me, THAT is a professional approach to the game that few can say they can or have adhered to.