Act as a seasoned email marketing strategist with 10+ years of experience in optimizing open rates. Your task is to explain the importance of a strong newsletter pre-header text and provide actionable tips for writing one that grabs attention. Cover the following: [1] Why pre-header text matters for engagement, [2] Key elements of an effective pre-header (e.g., clarity, curiosity, urgency), and [3] Common mistakes to avoid (e.g., being too vague or repetitive). Use real-world examples from [INDUSTRY] and tailor the advice for [TARGET AUDIENCE]. End with a checklist for testing pre-header effectiveness in [EMAIL PLATFORM].