General poll for organizing my tile sets.
I start with the walls to get a general feel/look for the interior I’m making. Then the floor, and then furniture.
And if I notice some furniture I want in there doesn’t fit, or if I want more symmetry, I adjust the outer walls again 
I start with the floor (usually several different floor types, I like variety), since that’s usually what we see the sprites on top of the most. If the floors don’t work, the whole level will be hard to read.
After the floors, I make the walls, making sure they contrast well with the floor but that characters are still readable in front of them. Then, with the walls as guides for vertical surfaces and the floors as guides for horizontal surfaces, I do the props.