“Eclectic” is the word people use when a room has not worked out. The rooms that do work usually have one thing holding them together, and it is rarely the period of the furniture.
Agree on material
An oak table, a willow basket, a terracotta lamp and a linen cushion will sit together whatever century they are from, because they are all doing the same thing with different raw material. Add one laminate surface and the argument starts.
Or agree on color
If the materials are various, hold the palette tight. Three colors across a whole room is not limiting; it is what lets you put a 1970s lamp next to a pot made last month.
Or agree on scale
A row of objects roughly the same height reads as a set even when they have nothing else in common. This is why a mantelpiece works and a windowsill usually does not.
Pick one, not three
The failure mode is trying to hold all three at once, which produces a room so consistent it looks bought in a single afternoon. One thread of agreement is enough. Everything else can differ, and the differences are what make it look like somebody lives there.
