Start slowly by chucking a few treats in it so the dog gets used to going and out. Encourage sleeping in it by putting him in when he settles in for a nap in the day. Make it cosy by covering it on 3 sides with a blanket and put toys inside. This makes it a nice place to be rather than a punishment. Start slowly, close the door for 2 mins, then later 5. Next day 10 and so on. Within a week he will hopefully be going in of his own accord for a rest. If he barks and performs, ignore him. When he goes in and out dont make a fuss, just make it normal. As someone else said, wear an old tshirt for a few days and then put that in the crate if you are going out