There are many forms of organization used by darts leagues around the world, so we've included a list of links to the Bylaws of several darts organizations.
If an organization is going to be of significant size, or if it is being formed as a Corporation or other legal entity, it is a good idea to consult with an atto ey about the legal requirements and wording of the organization's Charter and Bylaws.
New organizations might want to read through some of these, and pick & choose the types of features that they would like to use to gove their own club or league:
American Darts Organization (ADO), Bylaws: http://www.adodarts.com/wp-content/uploads/2013/05/ADO-Bylaws-2.pdf
Brunei National Darts Association, Rules & Bylaws: http://bnda.webs.com/rulesconstitution.htm
Grand Rapids Dart League (GRDL), Bylaws: http://www.grdl.org/Documents/GRDL_ByLaws.pdf
MinuteMan Dart League, Bylaws: http://www.mmdl.org/view/bylaws
Many more dart organization rules and bylaws are available on the Inte et, but these are some well-written versions that have been around for awhile.