Take a look at Linux User Group HOWTO (see below). Else, just go out with geek friends for some beer/coffee/whatever somewhere and launch a website to tell other people to join. If it is still active after some months, write us so that we could include your organization in the list. Avoid creating a new LUG in your city if another one is already active : it will split effort and most probably kill both of you.
To manage your LUG and learn more about the LUG topic, please take a look at Linux User Group HOWTO written by Kendall Clark and Rick Moen (also in Spanish and a depreciated howto in French).