P.S. pg also has a guide to lisp: http://www.paulgraham.com/rootsoflisp.html
I'm a fairly competent Lisper these days, but man I struggled so hard in the beginning and would probably have given up if it wasn't for PG's essays.
He also wrote a pretty good book on more advanced topics that's free to download:
http://www.paulgraham.com/onlisp.html
P.S. pg also has a guide to lisp: http://www.paulgraham.com/rootsoflisp.html