Once you have a square and are at the end of a knit row (right side), instead of turning your piece, take another DP (double point) and pick up twenty stitches along the left side of your square.

Take another DP and pick up twenty stitches along the cast-on side of your square.

Take another DP and pick up twenty stitches along the last side of your square.

You now have 80 stitches with 20 on each of four needles.

Using a fifth DP, work one row around the square (80 st)

Now you will set up your increases:

1. On the first needle - k1, m1, k18, m1, k1. (22 st)
Do the same thing on the other three needles. You are increasing one stitch on each side of the point of the square. There are two stitches in between the increases which will add a design element to the final piece.
At the end of this row you will a total of 88 stitches - 12 on each needle.

2. Work around on all the stitches. (88 st)

Repeat rows one and two until your rug is as big as you want.