The technique I use is to say something in the beginning of the story, as in Duke Nukem: Time to kick ass and chew gum! And I'm all out of gum. And then in the rest of the story, everytime a situation develops just say: Out of gum again! Obviously come up with your own lines. Or else introduce a catchphrase early in the story, and make an acronym (is that the proper english word?) For instance, in the army we had a phrase (excuse the swear word): A self organised military fuck-up. The acronym for this became Somfu. So everytime a situation developed we would just say: Not another Somfu.