Ribbons tied around curtain rings soften the drapery panels. They also help sweeten the room without locking in a specific look. image via here.
A vintage tablecloth with pom-pom fringe becomes a cheerful topper to a kitchen door window treatment. Image via here.
Cut a doorknob set in half, and push each knob into a plastic plug of a curtain rod you've wrapped with ribbon. (You may need to carefully enlarge the plug openings with a drill.
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All other images from here.