First, part the hair in the middle all the way down the back, if it is not already parted. A comb helps a lot to get it straight.:)
Then braid the hair on both sides, fairly tightly, and roughly just about the back of the ear. (But, if you are doing it on a person, you should probably start the braid right over the ear.:)) If you do not know how to braid, you divide the hair into three, and then take the left piece across the middle one. (It can be either side, but I am saying left just to explain. It is probably best to start with the piece closest to the face.) Now, the left piece is the 'middle' one (sorry if that does not make sense). Take the right piece, and put it over the 'middle' one. Now, what was originally left is 'right', what was middle is 'left', and what was right is 'middle'. Now do the same over again and again, taking the pieces in their new places as if that is where they have started (if that makes sense to you).