How would I make a mitered garter stitch edging in the round?

I am making one of those ubiquitous shawls with sleeves. Now that I am almost finished with the body of the shawl, I would like to pick up and knit all of the stitches around the shawl - which is basically a knitted rectangle and make a mitered garter stitch edging. Can someone please tell me how I would do this? I am concerned about how I would make mitered corners and a neat-looking garter stitch edging. I basically trying to knit a seamless mitered edging in the round, but I am going around a rectangular knitted objected. Thanks to those who respond with advice about this.

You might want to practice this to see if it will work for you, but I’d work to the corner, m1, k1, m1 at each corner. For garter in the round, you’d have to knit one round, purl one round, so you’d have to m1p, p1, m1p on every other round.