A headband is a satisfying project when you want a few relaxed rows, not a long stretch of counting. This one uses half double crochet through the back loop to make a soft rib, and its length is easy to adapt before you seam the ends.
Gather yarn and check gauge
Use worsted-weight yarn and a 5 mm hook; a wool blend or acrylic yarn will usually give the rib more stretch than cotton. The finished band is about 3 inches wide, with the length set to your own head measurement.
For a useful starting check, work a small swatch in half double crochet through the back loop. If your fabric feels stiff, try a larger hook; if the ribs look loose and gappy, try a smaller one.
Work the ribbed strip
Chain 14. Half double crochet in the second chain from the hook and in each chain across; you should have 13 stitches. Chain 1 and turn, then half double crochet through the back loop in every stitch across.
Repeat that row, keeping the turning chain loose and working the last stitch carefully, until the strip reaches your desired length. For a stretchy yarn, aim about 1 to 2 inches shorter than your head measurement; for a yarn with little stretch, work closer to the full measurement.
Join and check the fit
Fasten off with a long tail and bring the two short ends together without twisting the strip. Sew them securely, then weave in the ends. Try the headband on before trimming the tail, and undo a few rows if the fit pulls or feels too loose.