Don't let a single day pass without doing something towards your goal
The "chain method" is incredibly frustrating for me. After a first 2-3 slips I tend to quit whatever I tried to start, with incredible feeling of guilt. And slips are inevitable (the more I say I'll not slip this time, the more inevitable they become).So, I found something better: the accumulation method. I have a intermediate goal of, say, 10,000 push-ups. If I'll do only 10 push-ups a day, it will take me 1000 days to reach this goal — almost 3 years. Or I can do more — then I'll get to it faster. There is no frustration, I can skip any days I want, but if I want to reach this goal, I have to move forward.