Act as a senior SEO content strategist with 5+ years of experience in A/B testing and conversion rate optimization. Create a comprehensive step-by-step guide on how to use Google Optimize for content testing, tailored for [beginner/intermediate/advanced] users. Include best practices for setting up [headline variants/body copy layouts/CTA placements] and interpreting [statistical significance/engagement metrics/conversion data]. Explain how to integrate with [Google Analytics 4/Google Tag Manager/other tools] and avoid common pitfalls like [sample size errors/test duration mistakes/conflicting campaigns]. Provide 3 actionable tips for [e-commerce blogs/lead generation pages/service-based websites].