Before you begin...
With a pair of scizzors or knitting needle, poke holes around the edge of the towel about 3/4 inches apart from each other.
(The holes you poked will be used as the place to poke your crochet hook through to YO).
Poke your needle through the hole and chain 3 (counts as your first stitch), dc in the same hole chain 3 and 2 dc in the same hole. *Next, chain 3 and got to the next hole, 2 dc in that hole and chain 3 and 2 dc in the same hole." Repeat from *-*
Go all around the towel until the very last hole is filled. To end your border, simply chain 3 as usual and slip stitch it onto the first stitch.
That's all! Wasn't that pretty easy? I can usually get one down in 30 minutes or less. Provided I've already poked all my holes on the edge of the towel and I don't have to constantly jump up and run to help a hurt sibling or whatnot! :D