This is in my opinion the most versatile hem in sewing! It's used on everything from special occasion dresses and gowns to mens dress shirts. I've used this hem on wedding dresses and scarves. It is nice and clean and super easy to achieve!!!
For this example I am actually hemming a ruffle panel before gathering and attaching it. The skirt pictured is my Edith Wrap Skirt with In-Seam Pockets (available for PDF Download here). I recommend hemming your ruffle before gathering and attaching because its very easy to hem long panels and it reduces the potential for fraying while handling gathering.
Start by turning up the hem by 1/8- 1/4" (as close as you're comfortable with). Stitch along the hem line while maintaining the consistent turned up amount and sewing approximately 1/8" away from the edge. You will have the raw edge exposed at this point. You may trim loose fibers or any sections that are slightly thicker than others.