Currently I append the snippet below to prompts where I care about the resulting text. Just putting it in the context up front isn't as effective, and I assume if the overall prompt is large, or the context window is full, it will also be less effective.

> Use plain, clear, everyday language with a linear deductive flow; avoid hyperbole, juxtapositions, metaphors, analogies, punchlines.

I’ll try it thanks! I just got good mileage out of “don’t use ‘X, never Y’ format” on a document too, but I think linear deductive flow Covers it