If the Northern Hemisphere is your playground, and winters are grey and gloom, I bet I know exactly why your goals and resolutions don't last a snap.
Despite all our good intentions, it's just not inspiring to go out in the cold to go for a run, or zip to the gym, or refine our diets. The ways those things will stick are as follows:
1. You've had a strong epiphany, a do-or-die happenstance, or are flooded with constant support, influence, and fun.
2. You force yourself, despite your longings for warmth, comfort, and what you're used to.
January is not the time when I feel inspired to make changes. It's when I want to sit down by the heater, read books, cuddle dogs, snuggle people, and lick honey off my fingers. I want richer foods, and longer naps.
Spring is when I really zing.
So from here, I say stop with the January First goal-setting. If you're like me, make spring your "start date" for new undertakings - that is, if they are completely new to you and you feel some resistance. You know you want to do them, but you're not sure how or when, or would rather do it when it's not dark at 4pm, when fruit is fresh, when the air is full of fresh blossoms, and when there is a collective beam of health emanating from the world.
Things are born in spring. The death of winter may be the December solstice, but the true births don't begin until March.
Until then, conceive of ideas. Write them all out, in detail. Make a treasure map to your desires. Know you will do them, and make it easy for yourself. Figure out what will inspire you to stick with your chosen goals. Make your winter resolutions, too - but make those months about research, or tiny changes - on your way to your true initiation.
When I started my raw food path, I did not jump into it. I made it easy for myself. It was a Definite Do, but I wanted to make sure I would stick to it, and I wanted the tools to do so. I don't think I would have been able to do it without all my research. It's been almost 3 years now, and I have barely faltered.
For months, I poured myself into all the information I could on the subject. I obsessed, looking from many possible angles. There is a voluminous amount of options, and it is great fun to sort through them all, to find the niche that will capture your spirit. It takes a lot of work to swim through the choices, but make sure you know which one to focus on, because then you can commit.
You need to obsess to succeed. And you need to be specific.
If I had just said, "I am going to eat healthier" I probably would have slunk back to my old ways. Instead, I discovered the path that spoke to me, and I gave myself over to it.
I set dates, and I knew exactly what I was going to accomplish by those times. I had a network of people to inspire me, even if I didn't know them. They're out there. Find those people and read everything they have to say. Interact with them. Find communities. Fort yourself in library books. Earthquake your soul.
THEN, when the birds are out and the cherry blossoms are confetti on the ground, you know it's time to do it. The warmth of the world will call you out, and you can tap into the collective happiness that is awakening from hibernation.
You are fresh. New.
Consider yourself a newborn. You have to learn the basics before you will attempt to do more. So first...LEARN......choose...then Do.
and 
.
books, ALWAYS. - I still have a few to go.