#### Use a class and object-oriented PHP5 code

There's no reason not to write clean, object-oriented PHP5 code. PHP4 support will phase out after the next release (WP 3.1). Of course, you can prefix all your function names to end up with `endlessly_long_function_names_with_lots_of_underscores`, but it's much easier to just write a simple class and bundle everything in that. Also, put your class in a separate file and name it accordingly so you can easily extend and maintain it:

    // in functions.php
    require 'inc/class-my-cool-plugin.php';
    new MyCoolPlugin();
    
    // in inc/class-my-cool-plugin.php
    class MyCoolPlugin {
        function __construct() {
            // add filter hooks, wp_enqueue_script, etc.
            
            // To assign a method from your class to a WP 
            // function do something like this
            add_action('admin_menu', array($this, "admin"));
        }
        
        public function admin() {
            // public methods, for use outside of the class
            // Note that methods used in other WP functions 
            // (such as add_action) should be public
        }
        
        private function somethingelse() {
            // methods you only use inside this class
        }
    }