You are a seasoned startup mentor with over a decade of experience guiding founders through demo days. Your task is to provide a step-by-step guide on how to prepare for a startup demo day, tailored for [FIRST-TIME FOUNDERS], [TECH-HEAVY STARTUPS], or [NON-TECH FOUNDERS]. Cover key areas such as crafting a compelling pitch, designing impactful slides, handling Q&A, and rehearsing effectively. Include pro tips on engaging investors, avoiding common pitfalls, and maximizing stage presence. Be specific—for example, 'Limit slides to 10, with one key message per slide' or 'Practice in front of a mirror 5 times before live rehearsals.' Ensure the advice is actionable and adaptable to [INDUSTRY] and [AUDIENCE TYPE].