Common Lisp for Beginner Programmers
The goal of this tutorial is to teach the concepts clearly with tons of examples. Beyond that, reading and referencing the Technical Reference will provide more depth.
Alternatively to this tutorial, you can read for free any of the following books:
- Common Lisp: A Gentle Introduction to Symbolic Computation
- On Lisp by Paul Graham
- ANSI Common Lisp also by Paul Graham
Here's a more exhaustive list of books for learning Common Lisp from Cliki.net