Cast on 1 stitch.
Repeat these three steps until you have the required number of stitches.
It is important to remember that you are casting on 4 times as many stitches as you normally would for a garment or piece in the width you are making, and so you will need a lot more yarn for the cast on if you are using the long tail method. A good idea is to use two balls of yarn for casting on.
