The knit cast-on is used for its reversibility. The crochet cast-on would work as well.

Work all cast-ons and bind-offs loosely.

A slipped-stitch selvedge is used to keep the edges clean and to facilitate pick-ups. Refer to schematics for orientation of each square.

When picking up stitches for the next square, be sure to place the first and last stitches in the first and last possible points of the existing square, to ensure perfect linearity and a clean connection with center decreases above and below. If you work a few rows and discover that your edges are not squared up, or that the center decrease line is off kilter, start the square over.