Basically:

// plugin definition

$.fn.myPlugin = function(options) {
  var defaults = {
    key1: val1,
    key2: val2
  };
  // Extend our default options with those provided.
  var opts = $.extend(defaults, options);
  // Our plugin implementation code goes here.
};

To define more functions without cluttering the namespace and without exposing the implementation you shoul wrap your function creating a closure:

// create closure
(function($) {

$.fn.myPlugin = function(options) {
      var defaults = {
        key1: val1,
        key2: val2
      };
      // Extend our default options with those provided.
      var opts = $.extend(defaults, options);
      // Our plugin implementation code goes here.
    };
// end of closure
})(jQuery);

To provide public access to your function elements (for example options):

// create closure
(function($) {
  $.fn.myPlugin = function(options) {
     return this.each(function() {
      // Extend our default options with those provided.
      var opts = $.extend({}, $.fn.myPlugin.defaults , options);
      // Our plugin implementation code goes here.
     }
  };
$.fn.myPlugin.defaults = {
        key1: val1,
        key2: val2
};
// end of closure
})(jQuery);

Now you can change the defaults before invoking your plugin:

$.fn.myPlugin.defaults.key1= val3;
$("myDOMElements").myPlugin();

Useful links:

• http://docs.jquery.com/Plugins/Authoring
• http://www.learningjquery.com/2007/10/a-plugin-development-pattern