I've tried a few different books, including Land of Lisp, PCL, SICP, Chassel's Introduction to Emacs Lisp, but what I'd recommend head over shoulders above them all is buying a copy of Touretzky's Common Lisp: A Gentle introduction to Symbolic Computation. It's wonderfully thought through, really helped me finally grok elementary stuff like what a cons cell is, exactly how apostrophes function, what asymbol is, and a lot more. It's not meant to be comprehensive, it completely leaves aside CLOS, but it's left me with a damn solid foundation for working with Lisp.
Land of Lisp is fun, and the video is a must![0]; I also really like Norvig's PAIP (Paradigms of Artificial Intelligence Programming, available for free now on GitHub[1]). PAIP shows ways of programming in Lisp that really are unlike what I've seen in most other languages.
Lately I have been working the Exercism exercises and there are over 80 Common Lisp problems, with more problems being added over time (my hope is to finish what's there and then help by adding some more).
PAIP was my favourite, I recall not really liking Land of Lisp as I felt like the quality of the example code wasn't great, but I did enjoy the Dice of Doom implementation.
Depending on what you think is fun, I found the author of this intro to CL[0] very engaging and fun. I'd still run through gigamonkey's practical common lisp for something different alongside it.
Then you should be set to start tackling the boring nerd stuff.
I learned with Paul Graham's book, ANSI Common Lisp. Still have it somewhere. I also printed out and bound a copy of On Lisp, since it was out of print and he said to just download it.
It's better in print because then you don't need to swap between two apps on the same screen. Plus then you actually type out the code, which is a great exercise.
"This book should not have been published in its current form. It contains many instances of incorrect and inconsistent terminology, as well as many other errors."[1]
