Nothing beats experience.
I've recently started learning PHP.. and one thing I must say is..

Be consistent. If you're going to learn PHP, don't take long breaks in the middle.. all it does is break your tempo

I don't recommend (or atleast, I don't prefer) books, since they are static. PHP changes fast... books don't

I learnt my HTML/XHTML/CSS from w3schools... that is exactly where I am picking up the PHP basics from, as of now.

Also, if you already know Javascript.. then PHP should be easy enough for you, since there are some similarities between the two..