Ensure that he does not involve himself with brain stimulating activities such as playing video games before bed time. He should also not take drinks with a lot of sugar or caffeine as they inhibit sleep. In addition read him a story instead of letting him watch television and promise him a reward if he cooperates.
If he can tell time, make sure he knows what time he has to go to bed.
Whatever age he his, warn him a few times before he has to go to bed and tell him how many minutes are left.
Establish a routine so that it feels like he should be going to bed. Depending on how old he is, do something like get in pajamas, brush teeth, and read a story, or go up fifteen minutes in advance and let him have a quiet time in his room where he can do whatever he wants like read a book or something.