Things You'll Need
A fishtail swag is a simple curtain topper that adds an accent to the room and leaves your window open. It will give your window an elegant and breezy look, and it will accentuate the area around the window. Since it is relatively easy to construct, even the novice seamstress can make this simple valance on virtually any sewing machine..
Determine how much fabric you need. Measure the width of the window, then the side drop down to where you want the swag to end. To figure out the finished length add your window width, 2 times the length of the drop (for both sides) plus 12 inches to allow for the tail. For the width just use the fabric width. If you desire to line the swag you will need the same amount of fabric for the lining.
Lay the fabric out and trim off 10 inches diagonally on both ends to make a long trapezoid. Stitch fabric to lining with right sides together. Leave a small opening along one side to turn right sides out. Iron all edges. Stitch by hand or top stitch the entire panel. If you aren't lining the panel, just fold under 1/4-inch on all edges and iron, then fold again 1/4-inch, iron flat and stitch with a thread that will blend in with the fabric color.
Fold the fishtail swag in accordion pleats and drape across the drapery hooks installed at the top corners of the window. Make sure you have the longest edges on the outside and let the center of the panel droop nicely. If needed staple or thumb tack the corners to the wall to make the top tight. Tweak the panel to drape nicely.