Stockinette (where we knit one row, purl the next) is such a useful, simple texture. We do see it in stockings, after all, and, in miniature, in tricot jerseys or other garments. It's the texture most people automatically think of when they think "knitted."
It's a good stitch for production knitting. Many experienced craftspeople find they can work stockinette without looking, guided by touch alone. It's that automatic.
But stockinette likes to roll at the edges--that means at the bottom as well as at the sides. When you choose stockinette, be aware of this tendency. One of my favorite sweaters, a plain-vanilla stockinette mock turtle, uses the natural rolled edge of stockinette to good advantage: hem, sleeves, and neck all roll gently back on themselves. It's part of the design.
But what if, like my dear little mama, you want to knit a long scarf, in stockinette, and have it lie flat?
Then you are going to need a border, my dears. A simple one, a shallow one will do; three stitches will suffice if you choose them well.
Lady Folderol (featured on the right) uses seed stitch: k1, p1, k1 begins every row. You'll see seed on the edges of the ties in Lapped Hearts Neckwarmer. Seed stitch makes a good border for scarves, as well. It will keep your scarf from curling into a tube when finished.
Garter stitch (where you knit every row) makes a decent scarf border, although it can tend to pucker vertically. Steam blocking can counteract this.
Good old ribbing makes an elastic hem suitable for sweaters and vests, but if you choose it for a scarf hem, keep it really shallow. Two or three rows at the bottom and three stitches at each side will be enough to keep your scarf flat, and if it does draw in more than you'd like, then let the flat lady teach it a little discipline.