Choose yarn and a matching crochet hook
Make a slip knot
Chain enough stitches to fit around the head
Join the chain into a circle with a slip stitch
Crochet the first round in your chosen stitch
Continue increasing rounds until the circle matches the crown size
Stop increasing and crochet evenly for the hat body
Keep crocheting rounds until the hat reaches the desired length
Add ribbing, brim, or edging if desired
Fasten off the yarn
Weave in all loose ends