You can take cuttings from any growing tip of any branch or the main stem. At first the cutting will start to look "droopy", or at least stop growing for a few days. Within about ten days to two weeks the cutting will show new signs of life and growth as the new roots start to develope ("Party Time") - either that or the cutting will just shrivel up and die ("Bummer").
You also will want some sort of cloning hood covering the clones so moisture cannot escape. Since they have no roots they need to absorb moisture through their leaves (thats why they will droop). Also, the cutting will be hollow, make sure that no air gets inside of it, that's pretty much an instant death for it.