Don't set yourself up for failure by demanding things that you've never come close to achieving before. I realize this is antithetical to most self-improvement bullshit, but that's exactly the point. If you were already a viking, you wouldn't need to build a big boat. Start with where you are right now. Not with where you wish you'd been.
I have the will and the time to start a workout regimen but I've recently been beset by some pretty significant injuries that prevent this. Therefore, one of my new year's resolution is to walk 5 miles, 4 days per week. It's simultaneously small but ambitious. I'll be using the Runkeeper app on my iPhone to monitor my routine and you can keep up with me here. Here's hoping that 2012 will be a more healthy year than the last one.