Good New Year's resolutions improve you or your life and are reasonable to accomplish.
Don't just fall into the trap of writing down a list of regrets or things you hated about the previous year. Also don't obsess about an entire issue. Even if you are seriously overweight, don't just reverse the situation in your head and declare your intention to get thin. Choose a moderate weight loss goal of a specific, realistic amount.
New Year's resolutions that tend to succeed have several factors in common. First, you put some thought into it before January 1st rolls around instead of making snap decisions. Second, choose only one resolution or goal to focus on entirely as much as possible. Dedicate a year to it. Third, choose something that you can break down into installments or smaller objectives, from which you can formulate a plan of action to move through.
Willpower alone is rarely enough to get a job done. Having a course of action to take through chapters of some sort means that you have a series of specific steps that you can take in the direction of your desired horizon, and if you stick with it until January 21st, hopefully you will have formed the habits of action that take you to your win.