To get started you need:
bright contrasting cotton for tacking
cotton that matches your fabric
a blind hem stitch sewing machine foot
To make the hem:
Tack your hem in a long straight stitch with contrasting cotton. I have a cheap reel of red cotton I keep especially for tacking
Set your machine for blind stitch
now here's the tricky bit
Start with your tacked hem
you're going to stitch on the underside of the hem
I tried to take this pic to demonstrate how you fold the hem.
After that you just remove the tacking and you're done - just press your hem with an iron to give it a good finish. Being the genius I am, I forgot to take a pic of the finish product.