This is one of my shortcomings as a trainer so I'd love to hear what works for people. At one of my jobs, I give advice mostly. Some people look to me to give them willpower to work out, resist foods, etc. I can give them strategies but sometimes it's not enough. One person hates vegetables but wants to eat better. Another wants to give up diet soda but won't drink water. Diabetics won't give up sugar/carbs. There are many cases like that. To me, you're an adult, you just do it. Sometimes we just can't do everything we want to do and have to do things we don't. We all know the platitudes that it makes you feel better, healthier but that's not immediate enough. What makes you decide to make a change when you'd rather do something else? How do you develop will power?
For me, long term results work. I can give up short term pleasures if I know there is a pay off. I think of it as medicine and eventually it becomes part of your life and you don't even notice it, like my mom needed glaucoma drops twice a day. I hate eye drops but sure I'd do it if I needed to maintain eye pressure and not go blind.