Jean-Philippe Paradis over at HexstreamSoft has a very nice set of tweets on Common Lisp tips. For example, 【Meta+x】 slime-cheat-sheet opens a new frame with useful slime commands and their shortcuts. As Paradis remarks, this is virtually unknown—I sure didn’t know about it.
Another interesting tip uses the ldiff function to return the head sublist from member instead of the tail. Another thing I didn’t know. There’s a lot of good material in these tweets and well worth the time of any Lisper.
He also has some opinions that you may or may not agree with but, again, they’re interesting and he mostly gives his reasons for holding them. All and all a very nice resource.