Depending on when you want the code to be executed, there are several special passages where you can put it. Look here. If you have something that you want to be done or displayed at the beginning of every passage, just name that passage you created "PassageReady" for example
I believe PassageHeader and PassageFooter are better choice than PassageReady if you want to display content either before or after that of the current Passage, as PassageReady is designed more for executing background code before the current Passage is rendered.