What should I tell you once so I never have to say it again?

Help me write standing instructions for an AI assistant, the kind I save once in its settings so every chat starts with them. Don’t write them yet. Ask me up to six questions, one at a time, about what I use an assistant for, what annoys me in its answers, how long and how formal I want them, and when I’d like questions before an answer. Then write the instructions in under 120 words, as plain sentences that say what to do, with a short reason where it helps. Don’t give the assistant a role to play, and don’t use capital letters for emphasis. After that, tell me which line is most likely to backfire, and on what kind of request.