jQuery Plugin Boilerplate – Based on http://markdalgleish.com/2011/05/creating-highly-configurable-jquery-plugins/

jquery.plugin.js

/**
 * Accordion plugin
 *
 * @author XY (123 AG)
 */

;(function(window, document, $) {

    /**
     * Plugin name
     *
     * Used for $.fn namespace ($.fn[PLUGIN_NAME]) and options data attribute (data-PLUGIN_NAME-options)
     */
    var PLUGIN_NAME = 'accordion';
        
    /**
     * Plugin constructor
     *
     * @param {jQuery object} $element
     * @param {Object} options
     */
    Plugin = function($element, options) {
            this.$element = $element;
            this.options = options;

            this.defaults = {
                
            };

            // …
        };
    
    Plugin.prototype = {
        
        /**--------------------------------------------------------------
         * Pseudo-public methods
         * -------------------------------------------------------------- */

        init: function() {
            var metadata = this.$element.data(PLUGIN_NAME +'-options');

            this.settings = $.extend(true, this.defaults, this.options, metadata);

            // …
        },

        enable: function() {},
        
        disable: function() {},

        /**
         * Open specific item
         *
         * @param {Number} index Target element index
         */
        open: function(index) {},
        
        /**
         * Close specific item
         *
         * @param {Number} index Target element index
         */
        close: function(index) {},


        /**--------------------------------------------------------------
         * Pseudo-private methods
         * -------------------------------------------------------------- */

        /**
         * Some helper methods
         *
         * @params {Number} param
         * @returns {Number}
         */
        _someHelperMethod: function(param) {
            return param * 100;
        }
    };

    
    $.fn[PLUGIN_NAME] = function(options) {
        var args = Array.prototype.slice.call(arguments, 1);

        return this.each(function() {
            var $this = $(this),
                instance = $this.data(PLUGIN_NAME);

            if (instance && typeof options === 'string' && instance[options] !== undefined) {
                // Apply method
                instance[options].apply(instance, args);
            } else {
                // Init new instance
                instance = new Plugin($this, options);
                instance.init();

                // Save instance
                $this.data(PLUGIN_NAME, instance);
            }
        });
    };
    
})(window, document, jQuery);