Start by unpicking all the seams of the pillowcase. I did this as it meant I would have ready made hems and seams, and it added a tiny bit of length to the finished skirt. BUT you could just cut along the seams if you are feeling lazy and not too bothered about how short the skirt will become.

When you've unpicked the seams you will be left with one large oblong panel. Cut off the folded envelope bit so your left with one panels which should have a fold down the middle making two equal panels.

Cut along that fold line. Then sew it back together! Obviously this is a little tedious but it means my skirt had two side seams rather than just the one seam. You could skip this step and leave the panel as one piece and just have one seam at the back of the skirt. I personally much prefer two side seams!

When you have you two piece joined at one side you need to fold over 1/2" and press and then 1/2" again and press to make a neat hem. Then sew.

Now you need to make a casing. A casing is what the elastic will lie inside and will form the waistband of your skirt. First measure your elastic's width not length! (mine was one cm wide)
You then need to turn over 1/2" and press then turn over again by about 1cm to make your casing. Press that 1cm fold and sew as close to edge as you can.

You should now have a sort of tunnel in which you will thread your elastic through. If my explanation on a casing is a bit bleh try googling it someone would have found a better way to describe it. When you have your casing you need to figure out how long to make your elastic. Measure your waist or wherever you want your skirt to sit and take away 4" as it will stretch!

Thread your elastic through the casing gathering the material as you go. Make sure you don't lost one end of the elastic inside the skirt or you may have to start again. Pinning it at one end while you thread the other end through is a great idea.

When you've threaded the elastic through the casing you will have a gathered waist band. Now you just need to pin the final side seam together (make sure you leave the pins in the elastic!) and sew!

Enjoy your new pillowcase skirt!