As far as television and movies are concerned, all non-corporeal beings seem to have a firm footing on the ground they walk upon yet can walk through walls and pass through all other solid matter on our three dimensional plane. This seems to be the case whether they’re ghosts, spirits, poltergeists, demons, people from parallel Universes not totally phased into our reality, or just humans whose atomic structure has been altered in some way to take away their physicality in our Universe.
In reality ghosts and other beings lacking complete physicality in our world tend to appear to float about most of the time and they don’t necessarily always float above the floor all the way. Sometimes their legs appear to be cut off. Ghosts are often extremely confused spirits and will inadvertently gain traction on a surface and walk when remembering their life as a human. When ghosts and other non-corporeal beings are intelligent with a clear mind then they can learn to phase parts of themselves into our reality so they can indeed walk upon a floor or touch objects, including violently flinging them across a room in a rage.
In addition, ghosts and other entities not of pure evil can walk upon the hallowed grounds of graveyards, churches, etc. The sites of their death is also considered hallowed ground and there their power is strongest and the soles of their feet are horizontally solid upon surfaces for brief periods of time.