When we set goals for ourselves, we set goals that will challenge us, make us step outside our comfort zones (at least, I hope you do =)). But when we do that, the goal seems overwhelming. We scare ourselves into thinking we can't do it.
The key to completing those goals is to take it one step at a time.
Losing 50lbs is daunting. But if you break it down into smaller steps, it becomes easier. Losing 1lb a week is easier. It's even easier if you set how you're going to do that. For example, cutting out 1 soda a day, parking at the back of the lot and walking to the store, taking the stairs at work instead of the elevator, eating more veggies at dinner instead of the main course...
Want to start running? Start with working up to 30 minutes of walking. Then start adding in a minute or two of running. Pretty soon your running time is more than your walking time.
You don't have to focus on the end goal, just the step that's in front of you.
Let others know what your goals are and let them encourage you along the way. By the end of the year you'll be able to look back on what you've accomplished and see how far you've come.