Chop off bottom of dress, making sure it's long enough for your tastes and roughly 1.5 times your hip measurement, just hold it against you don't bother measuring.
Grab some wide elastic (this is 3 inches wide) wrap it around your waist (wherever you want the skirt to sit) and overlap it slightly (2 cms approximately) then cut it.
Now for your easy peasy waistband, overlap the ends of the elastic, at least an inch. I overlap more than I included in the original estimation to allow for easing up of the elastic with wear, you don't want it to go baggy.
You don't need to stretch the elastic as you sew but you'll need to use a zigzag stitch, a regular stitch length of 2.5 will do. Now stitch the overlapped ends of the elastic, I did this 2 or 3 times about 1/2 a cm away from each stitch line. You're just trying to make sure that the elastic stays together and sits flat with no flappy ends.
See it sits flat!
Next you need to make the skirt piece the same width as the elastic, so with a long stitch length (I used 5mm) and roughly 1cm away from the raw edge stitch with a straight stitch, don't get hung up on sewing too straight, these are just gathering stitches. Once you've gone round once, cut the thread (leaving a couple of inches) and stitch round again just to the outside of the original stitch line.
Grab a seam ripper and lightly pull on the stitches starting at the start/end point, this will start to gather the skirt, line up the elastic with the skirt and keep pulling on the stitches until the elastic and skirt are the same width. You want the gathering to be even around the skirt.
Now pop the elastic waistband over the top of the skirt as below. For neatness sake line up the elastic waist join with the side seam of the skirt piece. If you stitched the elastic together properly it should sit flat both sides so it doesn't matter which side is facing the skirt as you sew.
Now stitch the waistband to the skirt with a zigzag stitch again, I just stitched over the two gathering stitch lines you made initially. Stitch all the way round and continue stitching a little over the starting point, back stitch for a couple of stitches then you're done with the sewing.
This is what it will look like
Now you need to remove the initial gathering stitches, I'm lazy so I stretch the waistband of the skirt which will pop the straight stitches (because straight stitch is NOT a stitch you should use on stretchy fabric except for gathering) you can then just pull out the stitches with a seam ripper or they will show as below pic.
Last step flip up the waistband and the raw edges of the skirt will be inside the skirt, and since you've used a hemmed piece of fabric your skirt is done.
I'm a busy Mum and make these tutorials instead of catching up on much needed sleep so if this is useful to you be sweet to me and just leave a kind word of thanks.