Grady Mathews first learned how to handle a pool cue at age 13. More than 30 years later, despite his status as a pro, he's still honing his game.     It doesn't matter that Mathew's has won three world championships, matched shots with Paul Newman on the silver screen, appeared 40 times on national TV and been profiled in newspapers and magazines.     It doesn't matter that he's known as the world's best one-pocket pool player, or that his knowledge of pool runs from deep to profound. He teaches, sells cues, recovers tables, stages trick- shot exhibitions, makes instructional tapes and even writes philosophical-psychological columns for billiards publications.     But fame won't win a tournament. In the book of Mathews, hard work counts as much or more than experience.     Most days he rises with the roosters to practice his craft, shooting alone for better concentration. "One of the biggest problems with pool players is they don't make the effort to correct their mistakes. In pool, the most-prepared win the most. It takes dedication.     Nine-ball takes about 5-6 years to be competitive. One-pocket takes 20 years to compete at the championship level".     The dedication has paid off. Mathews has won the one-pocket world championship in 1983, '84 and '85, and commands $800 to $1,500 in appearance fees. His notoriety earned him a spot in the movie, The Color of Money.