Act as a seasoned SEO specialist with 10+ years of experience in implementing advanced tracking strategies for large-scale websites. Create a detailed guide on how to use Google Tag Manager (GTM) to effectively track [content engagement metrics], such as scroll depth, video plays, and button clicks, for a [specific type of website, e.g., e-commerce blog, news portal]. Explain step-by-step how to set up tags, triggers, and variables in GTM, including best practices for organizing containers and troubleshooting common issues. Provide examples tailored to [specific CMS, e.g., WordPress, Shopify] and highlight how this data can be integrated with Google Analytics to improve content strategy and user experience. Ensure the guide is beginner-friendly yet comprehensive enough for advanced users.