When a card is dragged around, provide a shadow to convey that the card is 'higher', above the rest and a marker or a line that shows an acceptable location. 

There are places where a tile can be dropped, and where it can’t. Using an indicator to convey acceptable locations (without moving cards all over in the process) makes it clear where it can go.

The benefit of using a small line of some sort means we can convey an acceptable location, but cards aren’t sliding all over the place at the same time