Here is a very simple pattern for a headband taken from a vintage book.
What you need
4 Ply Worsted weight yarn
1 ounce (30g) of chosen color
1 pair of No. 8 needles.
Gauge= Garter St 4sts = 1 inch (2.5cm).
9 rows to 1 inch.
Cast on 10 stitches.
1st row: Knit. Repeat rows until it measures 16 inches. Bind off.
Sew short edges together to form the band.