What you need:
1 yard of cotton or voile fabric (I prewash mine when making pillowcases)
thread and other sewing notions
sewing machine
1. Line up your selvages, square the right side of your fabric, and trim to 30 inches long.
2. Fold the fabric WRONG sides together so that you have a rectangle that measures 19 inches tall by 30 inches wide. Overlap the selvages. Pin raw edges together.
3. Sew along each raw edge with a 3/8" seam allowance. (See above picture.)
4. Turn pillowcase inside out (so now the right sides are together) and poke out corners. Press seams.
5. Sew along each side again, encasing raw edges, with a 1/2" seam allowance.