I'm really going out on a limb by disagreeing on a topic that everyone in the world seems to agree on: new years resolutions. The idea of starting the new year with a new and improved mindset just seems so obvious, so you may ask why do I have to annoyingly disagree with everyone on this topic?
Setting a new years resolution in the first place requires premeditation. You have to think in advance about what you want to change about your life, but if you want to change something about your life you need to change it starting now. The second you decide something is worth changing some action must be taken; it can't be put off until a later date, there's no reason for it to. If you can admit to yourself that something is wrong why would you conciously continue to do it? Benjamin Franklin once said "Don’t put off until tomorrow what you can do today."
Lastly but in my opinion most importantly: by labeling a specific goal as a new years resolution you are unknowingly assigning it a significance it does not deserve and should not have. This artificial and self-imposed rank subconciously affects your perception of how difficult that task really is and how much effort it will take to start your journey towards it. For example, if you want to lose weight, just start eating a little healthier day by day; maybe the next time you go to the Costco food court and get a hot dog, just use the soda cup for water. Gradually implement positive change into your life and eventually you will be on a path to your most-desired goals. The people in your life who you've noticed lose a lot of weight normally don't tell you it was all because of a new years resolution; it was gradual change to their lifestyle. That is why gyms fill up in January and are mostly empty by February. All the new years resolutioners couldn't keep up with the huge sudden change that they imposed on themselves in less than 24 hours and eventually gave up.
Change needs to be gradual and you need to treat it non-challantly. Don't give something that could be a small lifestyle change a daunting significance in your mind.