Great question. Generally I do one of two things. If I know I'm going to be out late or have plans for the night I make sure that I do my dishes and journal entry before I head out. It isn't the best solution for me but no one wants to write for an hour when they come home from a night at the bar. The second is as Shea LeBeouf would say "just do it". That's the thing with discipline it is there for you when your motivation is not. And you know what? If you miss a night it doesn't matter. What matters is if you pick it up the next day and continue doing it. Not everyone will hit every day not everyday will be optimal.