Where I learned to fly they mixed MOGAS in with the AVGAS, attempting to lean that caused the engine to stop, so fully rich in all stages of flight and altitudes. One guy 400+ hours decided to lean the engine at 6000', the engine stopped, and he descended, it took him until 4000' before he got it restarted.
On another point, flying in California during the summer, if you didn't lean the engine for taxi the plugs fouled before we got to run ups, sometimes they would foul up if they were leaned and you were at a high altitude airport (1000'-2000' amsl) and a couple of times we couldn't burn them clean and had to taxi back to get a mechanic to actually remove and clean them.
As has been said before operate the aircraft to the POH.