Once again I have found the best way to learn is to go to the source. If you really want to learn something you have to find dig into the implementation, read the classics and seek out the originators. In my quest to better understand the lisp I came across this C2 lisp resource with tons of great info. I have spent a lot of time researching common lisp online and this is one of the best collections of info I have found.
Also the discussion page is full of gems.