Pattern:
Cast on 40 stitches.
Row 1: Knit
Row 2: Knit to within last 2 stitches. With yarn in front, slip last two stitches as if to purl.
Row 3 and 4: Repeat Row 2. This gives a nice garter stitch border at the bottom, and the skipped stitches at the side edges make a smooth, rounded selvedge.
Keeping 2 stitches at each edge in selvedge pattern, work the following pattern on the center 36 stitches:
Row 1: *k4, p2; repeat from * across.
Row 2: *k2, p4; repeat from * across.
Row 3: Repeat row 1.
Row 4: Repeat row 2.
Row 5: k2, *p2, k4; repeat from * across.
Row 6: p2, *k2, p4; repeat from * across.
Row 7: Repeat row 5.
Row 8: Repeat row 6.
Row 9: *p2, k4; repeat from * across.
Row 10: *p4, k 2; repeat from * across.
Row 11: Repeat row 9.
Row 12: Repeat row 10.
Repeat these rows until desired length, or just shy of square. By the time you have completed one repeat, the pattern becomes mindless, and it's easy to see where you're at.
Finish with 3 rows of garter stitch, still maintaining selvedge. Cast off as desired.
I like to use the sewn cast off, as follows: Leave a tail at least three time as long as the piece is wide . Thread a blunt needle, and sew through the first two stitches on the needle, from right to left. Sew back through the first stitch, from left to right, and drop that stitch from the needle. Repeat, always going through two, and then back through one.