How long have you been doing this? One single pixel line of the shade color beneath the platform, nothing more.
Actually not. I for example use three pixel line beneath overhangs, one dark grey and two lighter but yet darker than the base grey. You can use just one, thats adequate but there is room to manuvre. However you cannot do it like done in the orginal attempt of this drawing where the overhang shaddowing is not just the lines directly above the overhand but making some sort of round patterns.