Well, here is how I do it, a friend gave me this advice. Place the starting end of the elastic in between the 2 layers of fabric and pin it in place. Then lay the elastic where you want it and pin around it, sort of making a little pocket or sleeve around it...like this"
The " - " is the pins, and between them is the elastic inside the fabric....i hope that isn't too confusing. Then what you do, is do a small lock stitch on the pinned end on the elastic, then pull and stretch it from the loose end, it should slide easily through the material. While holding it stretched do a zig-zag stich all of the way down. The pins hold the elastic right where you want it. at the end, do a small lock stitch again and cut the extra elastic.
Hope that helps, it makes it a snap to apply elastic, and makes it go so much fabric, plus eliminates the guess work of whether or not you are getting the elastic in your stitch or not.