One of the most common—possibly the most common—New Year’s resolutions people make is "this year, I will lose weight." It is also one of the most commonly abandoned. People go into it full of good intentions, but somehow it doesn’t seem to happen. It’s not a problem of lack of discipline or will; often, it’s simply a matter of the words being easy to say—particularly in the heat of holiday overeating—but actually following through turns out to be a lot more difficult.
There are things someone can do that make it easier. Setting a specific target is one. Rather than a vague "lose weight," a better resolution is "lose X pounds" or "get under X pounds by a certain date, and stay there". Alternatively, the goal can be not a number, but a practice. The idea is something concrete and measurable, providing a specific course of action and a way of knowing if the resolution is indeed being worked on. Accountability is another motivator. Writing down the resolution, or better yet, telling a friend, lessens the temptation to cheat.
There are also some things it is important no to do. Setting unrealistic goals, or unrealistically strict regimens, can hamper efforts to be healthier by encouraging cheating, or abandoning the resolution entirely. Someone who falls short of a goal is likely to simply give up on the project entirely, and not be motivated to attempt to reach a target they know they won’t be able to. Things like constant weigh-ins or cutting out junk food—anything that makes weight loss a drag or a chore—also do more harm than good.
In fact, some experts suggest that making weight loss a resolution—even with a specific goal weight—may be one of the worst ways to develop healthier habits, for that very reason. By making weight loss seem like a burden and a mandate, someone who makes this resolution gives unhealthy behavior a forbidden-fruit appeal while instilling in themselves exactly the sort of negative emotions that lead people to turn to unhealthy comfort foods. Far better to just decide to eat better and develop a plan for that.