Don’t expect it to be successful on day 1. Or 2, or 3.
You don’t need bribery, though some kids benefit from rewards. The best encouragement I’ve seen has always been telling the kid he’s going to be a big boy who can go to school, not need diapers, etc. Don’t be upset at him if he has accidents, but do praise success. Also, don’t let him use a diaper part of the day and not others, or diapers when out. Insisting on using the toilet throughout the day is important. Take him to try every so often.
I’m sure others are going to say the exact opposite, but this was my experience :).