A prompt library works best when each entry captures a real task you repeat. Start with three tasks, such as summarising a status note, drafting a reply or extracting questions from a brief.
Save the prompt alongside a sample input, the expected output and the fields you need to replace. For a reply template, make the recipient, purpose and facts explicit placeholders. Keep a successful example and one example of output to avoid.
Give each entry a short version note. When a prompt begins producing inconsistent results, rerun the same sample with the old and new instructions. Change one thing at a time so you can tell which edit helped.