An easestitch is similar to a staystitch in that it is a simple straight-stitch, slightly-longer than your normal stitch but not a baste-stitch (e.g., if you're normal stitch length is 2.5, set your ease-stitch to a 3.5) across a single layer of fabric that doesn't create any seam or join. Unlike a staystitch, you do not want to fix the ends of your stitch. Generally speaking, easestitching usually comes in twos, where you create the first stitch just inside your seamline, and then the second easestitch parallel to the first at about ¼" in from that. So for example: if you're using a ⅝" seam allowance, you might put your first easestitch in at ½" (⅛" of an inch closer to the raw edge than your seam allowance), and then create a second easestitch at ¼" from the raw edge. Check your pattern, it will instruct you on the allowances for your ease-stitch.
|Click to enlarge|
When pin-basting a gather that has been ease-stitched, I recommend putting the pins in perpendicular to the seam (pointing toward the raw edge) and having them every ½"-1". As you stitch your seam, using parallel pins will release too much of your gather as you remove the pin in advance of the sewing machine needle, and cause you to lose your gather. Putting in lots of pins at short intervals will ensure that the structure you gathered will retain its shape.
To practice this, you want two scraps of unequal size -- the larger scrap should be a few inches longer than the shorter scrap. Take the larger scrap and create a fold in the center of it to bring the edges of the pieces to match the shorter scrap's edges (so that they are the same size after the fold. Then, use a ruler and a marking pencil to create two dots on each scrap the same distance from the edges (e.g. each dot is 3.5" from its nearest edge) with the fold in between them. When you unfold the larger piece, you will have a setup similar to my instruction video.