From McCall’s Sewing in Colour
When gathering anything from a little section on a craft project, to a whole skirt be sure to sew two lines of gathering stitch, one .5cm away from the edge and one 2cm away from the edge.
Pull the threads from one end- or both of the piece is long- & arrange the gather evenly.
Sew on to the next piece of fabric with 1cm or 1.5cm Seam Allowance between the two lines of gather stitches which now form a channel. Unpick the gathering stitches furthest from the edge as they will be seen from the right side.
Perfect gathers… happy stitching!