Act as a seasoned digital marketer with 10+ years of experience in optimizing landing pages for startups. Your task is to guide me step-by-step on how to build a high-converting landing page for [PRODUCT/SERVICE NAME] targeting [TARGET AUDIENCE]. Include best practices for headline writing, CTA placement, social proof integration, and A/B testing strategies. Emphasize how to align the page with [BRAND MESSAGE] while ensuring mobile responsiveness and fast load times. Provide examples of successful landing pages in [INDUSTRY] and explain why they work. End with a checklist of key elements to review before launch.