Treat them as a fellow human being. Show them how to do something as opposed to just telling them. Don't expect them to do things your not prepared to do yourself. Most of all, Paise them up for doing a good job.
get a good mix of fittings or screws, something small and fiddly, empty them all in a big pile and mix them up and ask them to sort them back into their respective boxes, you'll want a good dozen different sizes atleast. "Character building" my old mentor would call it. ...or just what phil says, that'll work too...
I have always treated people who work for me this way, I have taken on 3 school leavers to date, they have stayed with me for years before either starting up on their own, with my full backing, I even gave them work to help them along or traveling the world as one of them did. I have only sacked one person in 30+ years, he was in his 40s and a bully to the youngsters when I wasn't on site, I wouldn't put up with it so he had to go.