Sally Jupiter Costume (Silk Spectre I) from Watchmen

Step 12 Yellow Fabric: Making the skirt.

As I expected cold on Halloween, I specifically made my skirt much longer (especially on the sides) than the movie's costume skirt.

Cut the yellow fabric longways to a length much longer than you are around the hips.  Also, made sure the skirt is a good few-several inches taller than you want the skirt to be (with an even longer section in a soft Vshape in the very front for the smooth point).  Using the yellow thread, hem the bottom and each side of the fabric.  
Using either color thread, do a long stitch across the fabric a couple or a few inches from the top, do not backstitch or otherwise secure the thread, and make sure to sew all the way to the ends and to leave a tail of thread long enough to grab on either side.  This is where you will gather the fabric, by pulling the bobbin thread on either or both sides of the fabric (pulling the fabric away from the ends of the bobbin thread, and inward towards the rest of the fabric.).  
When the skirt is as gathered as you want it, pin it to the bottom of the belt, gathered where you want, with the middle point in the middle, and sew to the belt all the way around (using black thread).  Trim excess from the top.  The first picture in this step shows the excess I trimmed from the top and shows the gathering I did on this fabric. 

If you want the skirt to be wider around than the belt itself as I did, or if you are concerned there is not enough overlap, make sure to leave an overlap when you first pin the fabric to the belt, and then sew the velcro to the excess fabric's edge and to the inside of the belt on the other side (you can also use snaps, buttons, hook&eye clasps, etc). 

As you can see in the second and third pictures, I added a little more yellow fabric to the skirt to have slightly more fabric in the back, and I did not do so until after I added fasteners (step 13).

The second picture in this step shows the extra fabric.  As this is on the underside and will not show underneath the overlap I planned on the belt, I was lazy and kept the yellow thread on when I secured the velcro and reinforced the fabric at the top with several stitches.  

The third picture in this step shows the velco I stitched (using black thread) to the other side of the belt where the extra fabric reaches.