How do you stop the edges of your knitting from rolling in?

You can either add a few rows of garter stitch (which is knit every row) or you can do a few rows of ribbing (which is knit 1, purl 1). One of my favorite boarders to put on sweaters or scarves is the seed stitch (knit 1, purl 1 to the end of the row and turn your work, then you purl the knit stitches and knit the purls and you just keep repeating that every time you turn your work)