Before you try out this style, make sure you know how to do a fishtail braid. I think this style would be a good alternative to a french braid for anyone who has super thick hair and cannot make the strand additions very narrow.
Begin at the top with a small section of hair. Split it into two pieces.
Pull off a thin piece from the side of the right section (it doesn't matter which side you start with, but just so it matches the pictures, I said right). Cross it over top and add it in with the left section.
Pull off a thin strand from the left side, cross it over top, and add it in with the right side section.
Now gather up a new piece from off the scalp (like you would for a french braid, but thinner.) You will want to cross it over the top and add it in with the left side, but unless you also pick up a little bit of the hair that is already in your hand on the right side, when you finish braiding, the whole thing is going to slide down the head and gather up at the bottom. Look closely in this picture and you will see that I have gathered some new hair and taken a small portion of the hair that was already in my hand. Do not use any of the piece of hair that you have just added in from the left.
Now cross it over and add it in to the left side. Pick up a new strand from the scalp on the left.
Add in some hair from the left section already in your hand, but not the part you have just crossed over from the right. Add it in with the right side. Pick up some new hair from the scalp on the right. Add in some hair from what is in your hand already. Try to get some from the previous crossover (in this picture, you can see the thin blonde strand I'm adding in).
Cross it over the top, and add it in with the left. Try to keep the hair taught so it doesn't slide down the head. Repeat on the other side, add in a small piece including hair that has already been crossed over previously.
Continue in this manner until you run out of hair on the scalp to add in. Finish it off with the regular fishtail technique.