Cast on 2 sts, kfb both sts. (alt - CO 1, kfb - see which works better)
next row, k across
next row - kfb, k to last st, kfb.
Repeat these 2 rows until you get the width you want the scarf to be ending with the knit row. The width is measured from your cast on sts up one side, not across the sts on the needle.
next row - kfb, knit to last 2 sts, k2tog. knit next row.
Repeat these two rows until it's as long as you want; that's be easy to measure at that point.
next row - ssk (or BO 1 st) knit to last 2 sts, k2tog. knit next row. Repeat rows until there's 2 sts left - k2tog.