A prompt gives inconsistent results. How do you improve it?

Make it a specification: explicit role, single clear task, the exact output format, and constraints (length, tone, 'if unsure, say so'). Add two or three consistent examples to lock the format. Lower temperature for determinism. Then evaluate on a set of real inputs including edge cases, not just one example. If it still drifts, split a complex task into smaller steps. Treat the prompt like code — version it and test changes against a golden set.