Start by ironing your pillowcase to remove any wrinkles.
If you're using an envelope pillowcase, pin the opening area of the pillow (where you insert the pillow).
Measure and cut the ties to fit around your waist. Some people prefer long ties that go around the back and then tie in front. So adjust to fit your preferences.
If you're using binding scraps as I did, fold and sew them into ties. I folded the ends in, and pressed. Then I folded the sides towards the middle, I pressed, then I folded the entire strip in half, pressed and edge stitched it. Then I sew the ends closed.
Sew the opening in the pillowcase. Use matching thread as the seam will be visible on the other side of the pillowcase.
Lay your pillowcase flat on your table and then fold. You can fold in half or you can allow for a flap at the top as I did. I measured 4" from the top down for the flap, then I folded the flap down at that mark, then I folded the pillowcase to cover the flap.
With the pillowcase folded as such, place one of the ties in the inside corner of the top of the pillowcase, and pin to. Sew down to the pillowcase. Repeat for the second tie on the opposite side of the pillowcase.
Return the pillowcase to the table and fold it up again, as above. Flip the flap up. Pin and sew along both open sides to finish the apron.
Fold the flap down, over the front side of the apron, and press well.