I found the last few years that rather than setting myself up to probably fail by forcing January 1st to be a I WILL DO SOMETHING ALL YEAR STARTING TODAY kind of day, I start up new habits in Fall. For example, I'm on my second and a half's month of daily meditation. Yeah, I started at the beginning of October, wanted to see if I could do it for *just* a month, and then liked the results, so set it up to try for another month and so far, here I am at all those days in a row!
The gym and exercise, to be honest, is still a hard one for me to get back into consistently. Part of that is the strong dislike I have while doing it, and part of it is the time hassle that surrounds it (see "it's not an hour, it's two" post from a while ago) but I am managing to get in a daily "minimum" that involves me, in whatever I'm wearing, in my kitchen, watching some show, doing mini cardio (walking on the spot, etc.) This time last year I tried to get a swimming routine going but I think it tapered off around the holiday break (because the pool got busy with families and events) and then I didn't want to compete with the January resolution crunch.
But increasing my cardio is really something I want to do. I just don't want to try to start it on January first, you know? Oh, and while I'm thinking about it, to be perfectly honest, part of why it's hard for me to get into a regular gym or yoga practice, beyond the above is that I find my body is that much more prone to owies. I tried "daily yoga" at the start of december (not necessarily a class, there are a ton of videos online too) and my knee went out day two so I had to significantly reduce the amount I was doing.
There's also a part of me that sits here and yells at me that I'm just lazy. And I'm not a fan of that part of me, even if it's motivated me in the past. I'm not "just lazy" and even if I do have a lazy day now and again that's totally ok.
So yeah. If there's something you'd like to do more consistently, may I suggest you start doing that thing now so that when the new year starts you've already got a few weeks under your belt? You may not function like I do, however, but I've found for myself that the pressure of new year doesn't work in my favour.
Your mileage, may, of course, vary.