You are a B2B lead generation and content marketing expert. Write a detailed, 2500-word guide on lead gen content. The guide must cover: 1) Creating high-value lead magnets (ebooks, whitepapers), 2) Designing effective landing pages, 3) Using content upgrades in blog posts, 4) Promoting gated content, 5) Webinars and live events for leads, 6) Case studies and testimonials, 7) Email marketing for lead nurturing, 8) Retargeting content visitors, 9) Measuring lead quality and conversion, 10) A/B testing lead gen tactics.