To starch a collar easily and well, you will need a bottle of liquid laundry starch, like Sta-Flo, available in most grocery stores in the detergent aisle. Stay away from spray starch: it’s just not heavy enough for collars.
Take a small bowl, fill it half-way with the liquid starch, and cut it with just enough simmering water to make it the consistancy of cream. If your starch is too thick, it won’t penetrate through the collar.
Take your freshly-washed shirt, and dip just the collar in the starch mixture. Work the starch right through the collar. Squeegee the excess starch out with two fingers. Dip again and repeat. If you like, you can do the same thing with your cuffs as well.
Hang up your shirt to air-dry overnight.
Next day, press over your shirt with a medium-high iron with steam, saving the collar ’til last. You know the spray button on your iron? This is what it’s for. 🙂 Lay the collar out flat, mist it until it’s lightly damp on both sides, and, pulling the collar tight, press it from the points to the middle. Press hard, working in small circles to “polish” the starch until dry. The mist relaxes the starch; when it dries it firms up again.
After pressing it smooth and flat, fold it, mist the inside of the neckband, and work the fold and the curl at the same time. This is the tricky bit. Work from the center out, using the point of the iron on the fold while bending the neck around. When it’s done, it will be like ironing the middle of a hoop, and the collar will hold the circular shape on its own.
(You do the cuffs in the same way, by the way, ironing them smoothly ’round until they form a barrel-shape that holds up on their own. Never iron creases into a cuff!)