I’ve mentioned Jean-Philippe Paradis’ Common Lisp Tip Tweets before. He’s reorganized the site a bit and categorized the tweets so that it’s easier to find what you’re looking for. If you don’t follow him on Twitter, it’s worth stopping by his site every once in a while to check out the new tips.
My favorite new tip since my last visit:
CL tip: Indentation-saving trick: (multiple-value-bind (a1 a2 b c1 c2 c3) (multiple-value-call #'values (values 1 2) 3 (values 4 5 6)) ...)