Cut into 1-in. cubes that each have an eye. Smaller pieces of potato encourages plant to grow roots quickly. Let the pieces air dry for 24 hours. You can dust with sulfur powder to prevent fungi from attacking them. Shake pieces in a bag with a small amount of the powder until evenly coated. They are fine without sulfur if the soil they are planted in is dry and warm.
Growing Potatoes: A Beginner's Guide to Planting Big & Healthy Potatoes