Seperate a side pony into 2 parts.
Take a small piece of hair from behind on side of hair.
(The smaller the better.)
Cross that small piece over and join it with the other side of hair.
Take a small piece of hair from the alternate side and cross it over to join with the first side.
It should start looking loose like this.
Just keep going. Like I said, it may take awhile, but the smaller the pieces you use, the cooler it turns out!
I like to use the smallest hair-tie I can find. Usually clear.
The best part about this braid is that it's ok to be messy! I even like to pull it apart a little afterwards to give it more of a beachy mermaid look. It takes longer than a normal braid but it's well worth it.
My fishtail braid made me smile all day and I hope it makes you too.