The trick here is to not make them unrealistic and too difficult to achieve.
Ordinarily I chat to a couple of people every year at this time, who have decided a marathon is their goal, which is great, but they haven’t ran before or at least, not for a few years, so I will always suggest smaller distances first for example.
You need a short term goal and a long term one, and when you reach them, set higher goals, the key is to maintain motivation, so having nothing to aim for is just as bad as having a goal that is very difficult, above all, you need to enjoy what you’re doing, that way, it doesn’t feel like a chore.
We will all see the gyms etc. much busier for the first two weeks of the year, but then it goes back to normal, don’t be one of those people that has given up on their goals, simply by setting realistic targets that you can enjoy along the way.