Re-resolutions
You signed up for that Yoga class. You bought a (lightly used!) treadmill. You got the brochures for that trip you always wanted to take. But two month later, you've gone to one yoga class, have logged 5k on the treadmill and who knows where the brochures went.
Oh well, there's always next year, right? Wrong.
Here's a secret: You can set a resolution anytime, not just at an arbitrary day of the year where the earth happens to be in the same spot as it was 365.25 days prior.
This might surprise you, but those successful people you read about actually fail a lot. They probably have 10x the amount of failures as the do successful things. The difference though, is that they don't get discouraged, they keep going. They take lessons from the failure and say "Okay, oops, I won't do it that way again" and then use that to get better.
Maybe yoga just isn't your thing. Or maybe you need to try a different variation (Bikram, Yin, Hatha, etc.). I like running now, but I used to hate it (but I'd do it twice a month anyway.) It was a task, a chore, something that needed to be done, something that I did to lose weight. Then last year I discovered trail running. Everything switched. Being outdoors and on the trails was what I needed for it to resonate with me. Now I can run 4 hours on the trail like it's no big deal. I'm out in nature, seeing things, relaxing.. but also happen to be jogging at the same time. It no longer feels like work, but rather something I can't not do. I run 2-3 times a week now.
Start things often. Fail at things often. The key to this though is that you have to start. Making excuses like "hmm, better luck next year" is the easy way out. Try something different, make more realistic goals, and set new "resolutions" for yourself continuously throughout your life, not just once a year.