Cut the armholes, by measuring about 3" in, and 3" down from the cut on the pillowcase.
Folded then pressed the front and back neckline to form a case for the elastic. Threaded the elastic by attaching a safety pin to pull it through.
Using bias tape that I made from excess pillowcase on the armholes, I sewed along the armhole openings.
Sorry these directions were not more thorough, but if you are interested there are many great tutorials online - google "pillowcase dress tutorial". I read through a few and combined the parts that I liked to make this. If I made it again, I would probably stick to bias tape tied shoulders rather than trying to make straps. And I would use a contrasting bias tape.
Don't forget to check out other metamorphosis projects on Between Naps on the Porch.