The first step is to cut your piece of fabric to fit your head. Use a cloth tape measure, piece of yarn, or your fabric to measure the width and length you like. This project is very forgiving, so don't worry if something doesn't come out exactly as you meant it to. It will probably still work.
First, decide how wide you want your ear warmer headband to be -- the examples in this guide had a finished width of 4 inches wide. Double that to get the width of the fabric piece (eg, 4 X 2 = 8 inches).
To get the length, wrap a cloth tape measure around your head where you would wear an ear warmer headband. Take the measurement of the front edge -- from the point that is closest to your forehead at the top, to the inside corner of the bottom (closest to your neck), going all the way around. Add about 4 inches to this length. The examples here were about 11 inches long, so the piece of fabric to work with was 15 inches long.
Cut out a strip of fabric using those measurements. If you need help, draw a paper pattern first, or draw on the fabric with tailor's chalk (or blackboard chalk if that's what you have lying around).
To make the headband, fold the fabric strip in half, long edges together. The "right side" of the fabric (the side you want to show) should be facing out.
The folded edge is the front of the headband, closest to your face. The two short ends will be stitched together and go at the back of your neck.
Wrap the folded strip of fabric so the short edges are together at the back of your neck.
Pinch the edges of the fabric together at the top and bottom. Carefully take the headband off, then pin the strip at those points to hold the layers together.
Draw a gently curved line between these two points. This will make the headband fit more snugly around your head.
Take regular thread. Use a secure stitch like a backstitch to sew up the seam.
Trim the excess fabric to about a quarter of an inch. The excess seam material will be on the outside of the headband. You will finish it off with embroidery floss