I am pretty new myself to PHP and I decide to use a project to build up a knowledge of PHP. I chose a simple event lister from http://www.mevin.com/ which I am in the process of adding more features. The event lister started out basically just adding,copying events and adding a new user. I have added an options page, optimised the database, included a rss feed, more secure login and remember me feature. I have plenty of other ideas in the pipeline, such as social networking integration. I try and learn as I go along.
I have used various websites for help and advice including this forum.
http://www.developphp.com/list_php.php
http://php.net/quickref.php
http://phpsec.org/projects/guide/
http://net.tutsplus.com/tutorials/php/30-php-best-practices-for-beginners/
http://pelfusion.com/tools/how-to-debug-php-code-and-useful-php-debugging-tools/
http://www.gracesmith.co.uk/43-must-read-php-articles-and-resources/
I hope this is of use
Tracy