One tip I often hear is to try a reward system, i.e. reward yourself for completing a task with a treat or an activity you enjoy. That can provide a boost of short-term motivation.
Another tip I often hear is to rather than focus on improving your discipline/willpower, set things up so that meeting your goals doesn't require massive amounts of willpower in the first place. For example, if your goal is eating healthy, you might make sure to not keep junk food in the house, or you could prepare a bunch of ready-to-go healthy meals on the weekend. The idea is to make the desirable behaviour more convenient and the undesirable behaviour less convenient. In addition, if you turn a behaviour into a daily habit, it will require less willpower to do.