This headband is begun with a crochet provisional cast-on, then worked back-and-forth in your choice of three patterns with a 4-stitch garter edge on both sides. The end of the work is joined to the provisional cast-on to complete the band.

Materials
20g/80m mini skein of 4ply sock yarn at least 80% wool, cotton does not stretch enough. I used The Lucky Ewe 4ply Mini in Political for Celtic Plait.

Tools
3mm knitting needles; straight or circular as you prefer
Cable needle; recommended for beginners and for the Celtic Plait

For the crochet provisional cast-on only, not required if doing some other kind of provisional cast-on:
4.5mm crochet hook
Scrap yarn, about 1.2m, a smooth 4ply cotton is a good choice

Tension & Gauge
One pattern row (33 stitches) is approx. 6.5cm wide; the patterns are very stretchy

Repeat your chosen pattern until the strip can be stretched around your head to meet. For me this was 22 times, for a total of 178 rows or 50cm, with easily enough yarn for grafting (about 1m).