Go high. While some curtains aren’t quite complete without a pelmet or decorative rod, a lot can be gained through the simple elegance of a built-in rod or runner just below the architrave or the picture rail, as seen here.
If your room already has strong features, such as statement furniture or boldly patterned soft furnishings, building the curtain fixture into the wall higher than the top of the windows will make the windows appear larger without competing with the other elements in the room. This look works best with curtains that are a soft, subdued color.