Step 1: Get a bit of hair from each side of your head
Step 2: Cross right over left
It doesn't have to be right over left, of course. But for the purposes of this Instructable, it's much easier to say right and left than "this one" and "the other side".
Step 3: Transfer to right hand
Transfer both strands to your right hand. Keep them separate.
My technique: grab the original strand between index finger and curled middle finger. Then take the next strand by grabbing between curled index finger and thumb. This allows you, in the next step, to rock your hand forward and release the first strand.
Confusing? See the video below. I'll show you first how your hands will move (with nothing in them to braid), then on some scrap pieces of cloth. If it looks difficult, practice first! You will be doing this on the back of your own head.
Step 4: Add hair from the left
Pick up some hair with your left hand. I do this by sliding my index finger under both some hair not yet in the braid and the bottom-most lock of hair. (This hand position works with the hand technique demonstrated in the previous step
Step 5: Cross left strand and pass to right hand
Passing is shown in the video below (this is the same video shown two steps ago