Braids are relatively easy to draw, you basically need to break it down into it's components, two straight lines, and drawing a cross-weave between them so that parts interlock like the teeth of a zipper, only you're folding segments of hair underneath one another. The braid will vary with the type of braid you want, there are many, I usually just keep the normal three plait one since it's the easiest to draw.
The best example I've seen drawn is this one:
http://rah-bop.deviantart.com/art/Braid-tutorial-5269918It's the most naturalistic and the most accurate. You should never draw the braid with the two halves like a 'heart shape' it'll look like two halves of a seed sitting on a line. Each part of the braid should be 'interwoven' bit by bit like in rah-bop's tutorial, and the edges and inner part of each segment of the braid should be rounded off. It should also get thinner and smaller the thinner your braid gets and be fattest where the hair is the thickest i.e. from where the braid starts on the person's head, usually at the very roots of the hair. Rah-bop does it right. It is the best depiction of a three-plait braid that I've seen and it close to how I have drawn a braid myself.
~ Pyre