The idea of a "new year new you" can be very attractive for people wanting to change something about their lives. But the concept that you need to wait until a better time to start changing your life is limiting and wrong. The most common resolution seems to be starting a workout routine, which many then drop within a few weeks. Partly because people don't always count on how much something will take, and partly because people overestimate what they are able to do consistently in their normal, day to day life.
It is rather easy to say: "I am going to workout and eat healthier." But this statement or "resolution" is extremely nebulous. A nice theory that will likely stay just that, a theory. Making a habit change permanent takes a lot of planning, a good evaluation of your personal abilities, and forgiving yourself when you mess up.
For example, "I want to work out more" is probably not going to work. "I will go to the gym three times a week," is more likely to work. But "Monday, Tuesday, and Thursday I will pack my gym clothes and put them in my car and go straight to the gym after I get out of class or off work" is the most likely to work. For two reasons: 1. Specific Plans are easier to follow through with, and 2. Pre-packing gym clothes and taking them to work/class removes two obstacles that would otherwise keep you from going to the gym: packing gym clothes and going home/to the dorm before the gym. Though this takes a bit of thinking ahead, it can be done the night before instead of when tired after a long day.
If I am trying to eat healthier I don't say I will eat healthier after I eat this chocolate. I tell myself that my first snack option is carrots and hummus. If I still want something else after, I may have a small portion of that. I don't just say I want to eat healthier, I make specific decisions ahead of time and make sure I have healthy food on hand, instead of junk food or going out for fast food. If I want to wake up earlier, I need to go to bed earlier, and maybe put my alarm across the room and anything else that makes the decision easier to follow through.
A big part of planning ahead is acknowledging that we are human and have both mental and physical blocks that can keep us from doing things, but that these can also be circumvented. Personally, if I go home before I go to the gym, I am much more likely to just stay home instead of going back out. Additionally, if I am meeting someone at the gym I am more likely to go instead of procrastinating until it's too late to go.
But even the best laid plans get dropped and canceled, often for things outside of our control. Which is why it is important to forgive yourself for messing up. It can be really easy to miss a day at the gym. Or eat more cake/candy/chips than you meant to. And once you mess up what's the point right? You've failed. NO!!!!!! You messed up once, maybe twice. You are human, it will happen. But one step back before ten steps forward is still a progress of nine steps. Every decision matters and continues to matter even after you mess up. Giving up and eating the whole carton of ice cream is still worse than eating two bowls. Missing a day or two at the gym, or a week of learning a new language is still better than to just stop until your next New Year's resolution. That's about 50 weeks of missed progress because one week didn't quite work how you wanted it to.
While the mental freshstart a New Year can bring can be useful. The best way to add a new habit into your life is to just start it now, make a plan by breaking up a big goal into the small daily decisions and then make the daily decisions that help advance you towards that goal. Even if you have to "trick" yourself into doing them. There is no magical time to start something. The time is now.