A WordPress plugin class

class-my-class.php

<?php
/**
 * Class description
 *
 * @package Plugin name
 */

/**
 * Class My_Class
 *
 * @package Plugin name
 */
class My_Class
{
	/**
	 * Class instance, used to control plugin's action from a third party plugin
	 *
	 * @var $instance
	 */
	public static $instance;

	/**
	 * Adds all the plugin's hooks
	 */
	public static function init() {
		$self = self::instance();

		if ( is_admin() ) {
			// Put any admin's hooks and filters in here
		} else {
			// Put any frontend's hooks and filters in here
		}
	}

	/**
	 * Access to a class instance
	 *
	 * @return My_Class
	 */
	public static function instance() {

		if ( is_null( self::$instance ) ) {
			self::$instance = new self;
		}

		return self::$instance;
	}

	
	}
} // End class.

add_action( 'plugins_loaded', array( 'My_Class', 'init' ) );

If you need to add a hook/filter you can do it like this (at init() method) :

add_action( 'save_post', array( $self, 'my_save_method' ) );

So it will be attached using the static $self variable and can be modified by third party plugins.