How can I sew an elastic waistband like the one on the American Apparel Jersey Pocket Skirt?

I'm not sure exactly of the effect you want because I cant exactly see the waistband, but im thinking this is a kind of 'rouching' issue? That's when you sew more fabric over the elastic so it has room to stretch, the more you do this the more puckered look you can get. I hope that was somewhat helpful.