Start with a slip knot on your hook

Make sure the tail of the yarn is on the inside of the hair band and the working yarn is on the outside.

Start a single crochet by slipping your hook under the band and pulling the yarn up to the top then through the loop securing it to the hair band.

Like so.

Continue crocheting around the hair band. You may need to slide the stitches down to cover the band.

When you get to the end, join the last stitch to the first.

Like so.

Now you get to be creative with your stitch pattern. I chained three.

Then skipped one and single crocheted in the next stitch.

I continued that pattern until I reached the end the secured the last stitch with a slip stitch in the first chain.

Wa lah!

Here are a few I've finished. Their quick and addicting! I played around with the stitch patterns since I'm just really learning how to crochet!

Here's another way I was playing with the look. I started the same way but single chained the bottom stitch...

Then single chained the top stitch.

This is the way it will look. You can experiment to your heart's content!
Disclaimer: I am a beginner crocheter so if I've worded something wrong...sorry!