The reward method has been shown to work but a sweet after a workout isn't a good reward. A better reward might be to put some dollar amount in a jar and spend it after a certain amount of time. What you spend it on should also be something enjoyable and not self defeating like a cookie would be. It could be as small as hobby supplies or as big as a vacation. The point is to make it something that isn't going to sabotage. I am sure there are other ideas. There is a book that is pretty good. "The Power of Habit" by Duhigg. There is actually a great story at the beginning about an obese, recently divorced woman who transformed her life through habit. It isn't your typical go to the gym everyday story.