Tiebacks & Trimmings
A tieback holds the curtain back in a soft gathered shape, where a rigid holdback gives a more architectural sweep. Which suits the room depends on how formal you want the window to look.
Trimmings work on the edges. A braid down the leading edge or a border at the hem defines the shape of the curtain and gives a plain fabric a line to follow.
Both read at close range, so consider them alongside the fabric rather than after it.