Cast on an odd number of stitches using needles that are slightly bigger than needles you would normally use with your yarn. For aran yarn you might use 6mm needles; for DK yarn perhaps 5mm needle; for 4ply yarn maybe 4mm needles. Or you could have a more tightly knit scarf using the usual size needles if you prefer. Do a swatch if you are unsure what would suit you.
Once you have cast on your odd number of stitches, continue in this way:
- [K1, Knit into the stitch under the next stitch] repeat to last stitch, K1
- K2 [Knit into the stitch under the next stitch, K1] repeat to last stitch, K1.
Repeat these two rows until your scarf is as long as you want it to be, and then cast off.