1) Don't let it die just because you mess up once or twice. One of the hardest parts about resolutions is that they have to last all year to "count" apparently. So, after keeping your resolution for a few weeks, the first break feels like total failure, and the resolution fades into the distance. But there's always still a lot of year left to pick yourself back up. Maybe the rest of the year isn't "new" enough, but it's still good, really.
2) Be specific about what you want and how you'll get there. If you want to write a book, how much should you write every day? How much can you write every day? Will you take breaks? What happens when life gets in the way?
3) Allow yourself some "cheat days." Breaks. Rewards. Whatever you want to call them. I like doing this at the end of every month. That way, you can keep your resolution through the month to earn your reward, making you less likely to slip up earlier. Some resolutions are easier to keep than others, but for some, you need breaks. If you want to do something every single day, it's going to be easy to miss a day, then miss another, then quit. Build your breaks into your resolution.
4) I think the best advice I can give you is to renew your resolution as often as necessary. I kept a resolution by renewing it every month. That way, if you break it, it's less of a failure, because you can still have more successful months than failed ones. You can still keep your resolution for the majority of the year.
Here's one thing I never understood: when does the "New Year" get old? When I post this, it will be the second day of the year, but I'm writing it ahead of time. It's December 29th today. A day that doesn't count, because it's in that weird space between Christmas and New Years where time doesn't exist. I get that, I feel the same way most people do, but what about before this weird time? When does the year get old?
I've never really understood why we celebrate New Years in the MIDDLE OF WINTER. It's still very weird to me. We should have picked a better date, like, the beginning of spring would make the most sense. Even the beginning of fall, when the new school year starts. That always bothered me when I was in school. Everyone's going on and on about a "clean slate" or whatever, and I've still got homework from the previous year and haven't even finished the term yet. Bleh.
Anyway, what I mean to say is, you can create a new beginning for yourself whenever you want. It's easier when we're all declaring it together, like New Year's. But the year doesn't have to get old. Renew your resolution every month, and you'll have a much better chance of keeping it.
Happy New Year, and good luck!