Mark the buttonhole position on the fabric
Choose the buttonhole length based on the button size
Reinforce the fabric with interfacing if needed
Set up the sewing machine for buttonhole stitching
Attach the buttonhole foot
Place the fabric under the presser foot
Sew a test buttonhole on scrap fabric
Sew the buttonhole on the marked position
Cut the buttonhole open carefully with a seam ripper or buttonhole cutter
Reinforce the ends if needed
Check that the button passes through smoothly