and easy way to start is to look at things like Yahoo groups or MSN groups. see whats online in your area. some of these groups actually meet in person. if there aren't any that do, start your own group online, to attract members, see if any of your lfs will let you post flyers about the group, etc.
if youre interested in a specific type of fish, look for national or even regional chapters for that type of fish, see what might be available in your area, and if there is nothing, find out what it would take to become an official chapter of a larger fish organization.