How do I braid my hair like this?

Lay on your side while getting it done.

http://www.youtube.com/watch?v=gpmvSZwQ-YQ

Here’s a great braiding site. I’ve done mine upside down before, but never across. Not sure how that would work. If you don’t already know how to french braid your hair, you should probably practice it the regular way first. For learning how, it’s very helpful if your hair is wet.

I think you would do it like any french braid, except instead of starting by your forehead, you would start on the side of your head by your ear, and then instead of picking up locks of hair on the left and right, you would pick up locks on the top and bottom. Actually I think laying on your side or at least tilting your head sideways while doing this would be helpful, as @75movies said.

The technique is very similar to “cane row”, a type of braiding suitable for afro hair.