Posted for W Atkinson <Walter@advancedpilot.com>:

 As soon as the engine smooths out after start (10 seconds?), I lean as
aggressively as I can and still keep the engine running.  If you do this
slowly, you will see an rpm rise , then a very slight rpm drop as you continue
to lean a tiny bit more more.  This is perfect.  I do the runup at this leaned
mixture setting as it is more diagnostic.  You CANNOT takeoff with it leaned
like that because if you forget to put the mixture full rich, it will die as
you advance the throttle.  That's the fail-safe.  If you can apply takeoff
power and the engine does not die, it was not leaned enough.
 
 Walter