Subtle tricks that I've found. (these "tricks" aren't exploitative — exploits tend to get abused and fixed rather quickly... rather, these are things that are actually kind of helpful)
Adding a two spaces at the end of a line makes a line-break, and that line-break can be better than other line-breaks available (it's often smaller, and sometimes this is the only way to get a line break)
Two neighboring blockquotes usually run together. If you want to visually separate them, add an em quad space in between them.