Step 1: Tools and materials.
- Sewing machine
- Small piece of scrap material
- paperclip or safety pin
- piece of tape.
Step 2: Find a pillowcase and determine how it is sewn together.
Another way a pillowcase may have been assembled is that the top end (opening where pillow goes through) will be sewn first. The seam along the length would be sewn after that. When this is done there isn't a complete tube around the top of the pillowcase. This type of pillowcase requires extra work since you will not be able to pull your string all the way around the pillowcase. The sage colored (plain, no pattern) pillowcase is put together this way.
Simply look at the top end of the side seam of the pillowcase to determine how the pillowcase is assembled.
It is possible the pillowcase may not have a tube on the top. In that case you will have to create one by folding over the end of the pillow and sewing the folded end fast.