Interesting post over on the Lean Software Engineering blog, "There are no a priori best practices".  In a couple of sentences Corey lays out what I think being Lean is about.  What I get out of the 2 sentences are that you must ALWAYS improve.  You may be the best but that doesn't mean your software practices are the best.  In 2 years there will be a better way to do things.   Keep these things in mind as you adopt new practices, and don't be afraid to experiment.