I'm about to start a new project on PHP but I have been out of PHP development for 4 years and would like to know which are the established practices, libraries (I remember Zend Framework, PDO), security guidelines, etc. that are mature nowadays. I'm not planning to go with a big framework (symphony, cakephp, etc) since this is a small project.
Also on the server side, I remember apache/mod_php was the way to go on that time.
This is a backend project for a mobile app, so no need to HTML/javascript libraries.
Classic guidelines don't change that often. LAMP applications are still the same, except for new improvements that PHP 5.3 and 5.4 have added over these years, so you might look into new practices with lambdas and chaining that make code more dynamic (like Yii framework). For small project I'd take Kohana or Codeigniter