I have more pairs of pajama pants than I really need. I only really need a pair of cotton ones for summer, jersey ones for travel/mildly cold and fluffy ones for cold nights. I have like seven pairs though. So in an effort to make space in my closet I'm turning some of them into bloomers. It is actually super simple, though there are three major ways to do it.
Sew the covered end of the elastic down first then sew the row of stitching which is the bottom of the channel. About an inch before you finish the row, pull the elastic to the desired taughtness and hold in place while you trim it then pin it down at the end of the channel. Sew the end of the elastic down, then coax the last but of the channel in place over it and finish stitching it up.