I got started with a class \ vacation at the Trials Training Center in TN. They also have plenty of how-to's on their web page http://trialstrainingcenter.com/how-to-ride-motorcycle-trials/
Or if you get a chance take a class from multi-time National Champ Ryan Young. Your local club can make arrangements to have Ryan come out to your area for a class if there are enough students.
Riding a trials bike is fun but, my opinion, you must ride in trials events in order to get the full appreciation of how fine an art riding trials is and that the skills learned in competition will translate into improved riding skills in other modes.
Enjoy the ride.