Not only are mitered squares good for pretty corners, they can stand on their own as a decorative element and really look good when you incorporate a second colour or stripes, the angle of the rows stands out much better.
To create a mitered square you will need to cast-on double the number of stitches you want one side of your square to be plus one stitch. For my square as I want an 8 inch square I am using DK yarn and 4mm needles I cast-on 81 sts.
Row 1: knit
Row 3: knit
Row 4: dec row: k38, sl1pwise , k2tog, psso, k38
Row 6: dec row: k37, sl1 pwise, k2tog, psso, k37 continue in this manner until you have 3 sts left on needle.