To install a scarf valance, use a drill and hook that can be fastened with screws. Install the hooks several inches past the casing of the window. Using a carpenter's or laser level, check that the hooks are hung level.
Keeping the valance flat on a table or the floor, fold it in an accordion style with all the folds equal to one another. Measure the window's dimensions, and then fold it to the desired swag length on either end. Hang the valance on the hooks.
When laying out the valance, make sure to stretch it to its maximum length. After the valance has been folded, measure the fabric so that the swag hangs to just slightly above the window sill's surface. Use this technique on both ends of the valance. Then tie a decorative cord at this mark on either end of the valance.
To hang the valance, hold the valance with the back side of it facing the window. Lift the valance so that the corded valance swags are even with the swag hooks. Gently hang the valance from the swag hooks at these corded sections. The center portion of the valance should now hang lower than the hooks to drape over the top of the window.