The practice: Tell Claude explicitly what you don't want, not just what you do want. Include a "Do NOT" section in every prompt where you've seen disappointing results.
Why it works: Without negative constraints, Claude defaults to the most common patterns in its training data — which for sales writing means corporate buzzwords, passive voice, and generic openers. Telling Claude "Do NOT start with 'I hope this email finds you well'" removes that entire pattern.
Highly effective negative examples for sales:
• "No: 'I wanted to reach out', 'Just circling back', 'I know you're busy'"
• "No: 'game changer', 'synergy', 'leverage', 'best-in-class'"
• "No: feature lists — only business outcomes"
• "No opening questions in the subject line"
• "Do not start any sentence with 'I'"
The principle: The more specific your negative examples, the more useful the output. Generic "avoid corporate speak" produces less improvement than specific "never use the word 'excited' or 'thrilled'".