The quality variation of the forums actually makes me go for books first - the author is accountable, therefore, usually checked information and structured the book to match its target group's eg. beginners) needs.
Then if you need more advanced, interactive or supplementary advice, you can still turn to forums, open-source communities, etc.
It is easy to master PHP and MySQL for those who have good understanding of how things work in web.There are lots of online tutorials available for the beginners.The following are online tutorials: php.about.com w3schools.com staffkit.com e-learningcenter.com
The best way to learn php or any language for that matter is to build something. Don't set your sights to high, just think of a simple script you want to build. A guest book for example. Decide what you want the script to do, then research how your code will work.