There are two basic types of swags, according to Drapes Made Easy: staggered and standard pleats. In standard pleats, all pleats come from the same point. Each staggered pleat begins somewhat further in from the preceding pleat. The depth of your swags should be one-fifth the length of your drapes.
To make a standard swag, begin by folding your piece of fabric half across its length. Press the fold using an iron and cut the sides of the fabric diagonally. The upper side should be narrower than the lower side. Unfold the fabric and mark off pleat positions on both sides at 5-inch intervals. Pin the fabric onto your worktable.
Beginning from one side, move the first pleat to the top and adjust the cloth in the fold to form a neat arc to the center of the fabric. Pin the pleat and repeat on the opposite side.
Repeat the process for the remaining fold marks and ensure all the ends of the folds meet in the same position.
For a neat look, adjust some of the pleats. Some might be too thin while some are too fat; others might be too low and others too high. If the pleat lies too low, pull it outward. If it is too high, pull it inward. Adjust a tight pleat by moving it in.