Make sure that club handle grips are replaced as needed, or consider larger/softer grips.
Reduce grip pressure on the club handle.
Avoid the strong grip position by rotating the left hand counterclockwise.
About the Author
Larry Foster, M.D., F.A.A.O.S., is a board-certified orthopedic surgeon who calls himself "a bad golfer, but a good golf orthopedist." Dr. Foster's enthusiasm for golf has earned him the nickname "Dr. Divot." Dr. Foster trained at Columbia University and the Hospital for Joint Diseases in New York City. He is the author of "Dr. Divot's Guide to Golf Injuries."
More Info on Trigger Finger
For a more in-depth examination of trigger finger, see the entry from the About.com Orthopedics Guide.