What's the best way to learn LISP?

Try reading Practical Common Lisp, by Peter Seibel.

My personal favorite is Abelson & Sussman Structure and Interpretation of Computer Programs. It uses Scheme, which is a nice and clean dialect of Lisp.

If you like a more practical approach maybe you should pick some Lisp framework for web design (I have no idea if such a beast exists) and jump right in.

You might want to start with The Little Schemer as a warm-up. It's not a practical book about writing production Lisp programs, but it's a great book for learning how to think in Lisp.