I follow essentially the same procedure as IO540, with my O360, and have never had any problems on start up. I was always trained to lean very aggressively during all ground operations except during run up.
The only thing I might add, and this only a preventative measure; when the mixture is pulled to ICO, and as the engine dies, close the throttle completely. It will reduce the shuddering as the prop stops, and will at the very least help prolong the life of your engine mounts.
A bit off topic I know.
Regards,
W.B.