You may use fine yarn or heavy, with small needles or coarse - depending on the weight of the yarn. It is an excellent way to use leftover yarn.
Cast on two stitches:
Subsequent Rows:
Continue as above, always knitting off the 1st stitch and increasing on the 2nd stitch, then continuing with the plain stitch (garter), to the end of the row.
When the finished edge of the blanket measures about 32 or 33 inches (this will be half the blanket), start to decrease.
To Decrease:
Knit 1, k2tog; continue to knit to the end of row.
Continue above each row until you are down to the end.
You will have a blanket 32 or 33 inches square, with a finished edge that is good looking.