What keeps me from relapsing is reminding myself what alcohol reduced me to. I can't imagine anything worse than going back to that. Continuing to remind myself how much healthier and better off I am seems to keep me away from it. I still get the urge to drink but, unlikely previous times that I've tried to sober up, I know for sure now that it's not at all worth it.
When I want to drink, I tried to find something healthy to eat or a new exercise to do. I try to find something that will benefit me in the long term, as opposed to drinking alcohol which will only fool me into thinking I feel better and only for a short period of time.
Another thing that's often helpful is going to places like this online and venting your thoughts. Staying sober alone can seem impossible sometimes and fortunately there are people out there eager to help.