Cover the crate with a blanket to create a cave effect. Reward your dog with a treat and praise. Practice this at least 20 times to reinforce good behavior.
Feed your dog in the crate with the door open, then gradually withdraw the food. by that time your dog is already used to the crate and he/she will be more willing to go inside it.
Initially encourage them in with food (try feeding them in the crate), with the door open, until they are happy to be in there, then gradually withdraw the food.