I started running for the first time in more years than I can count and while it seems every joint and muscle in my body hates me for do, I am pretty excited to get myself off to a solid start this year. It isn't easy to stop sleeping in and wasting the daytime hours when you close the bar and get home at 3 AM and play shows all week - without a routine exercise is hard to plug into the mix.
Here is my advice: Don't bog yourself down with expectations before you develop a habit. Don't tell yourself you're going to run 5 miles because you won't. Don't say you're never going to smoke again if you have tried that before and failed. Don't say you're never going to eat sugar again because that's asinine.
When we try to make changes we have to remember that it doesn't happen overnight and if you put levels on yourself before you figure out what you're capable of, then you're just setting yourself up to fail. Get the habit you want down (or start working on the habit you want to get rid of) and then worry about how to quantify your progress after you get started.