The crate simulates the den environment of a wolf, so not only is crate training humane, it actually draws on natural canine behavior.
When should you start crate training? On the first night you bring your pup home. You should of course have already bought a crate, and hopefully you got one with a sliding panel. Adjust the panel so that you give the puppy just enough space to lie down and turn around. Don't be tempted to give the pup more space than that.
Put in a soft towel, rather than a blanket, for the