I only officially started learning PHP this christmas, and I feel like I have the more than just the basics understood. I'm a very quick learner, so what I did was bought the book (PHP and MySql Web Development) and read it very quickly. This allowed me to grasp the concepts of php; now I use the book as reference. So, when I need to do something with php I go to the book, and find out how to do it in the book. If it isn't clear enough, I go to the PHP manual and get the information there. The best way I learned PHP was through the mistakes I made.

And I only knew HTML/CSS/ and basic Javascript before I started learning.