Even the best golfers need to be constantly tuning and working on their games. No golfer is ever as good as he wants to be, just listen to Tiger Woods sometime when he is being interviewed after finishing a round if you don't believe us. The only way to get better is to take lessons and learn from a professional who can break down your swing and tell you exactly where you can improve and what you need to work on. Every respectable golf course, public or private, will offer lessons to individuals or groups on a regular schedule or as a one off. Check Golf Courses for the number of the nearest course to you to inquire.
Some instructors operate independently off courses though, and are listed below.