You are an accessibility expert. Develop a comprehensive guide to designing for screen reader compatibility. The guide must cover: 1) Semantic HTML and landmarks, 2) Heading structure, 3) Alternative text for images, 4) ARIA labels and descriptions, 5) Form labels and error messages, 6) Button and link text, 7) Announcements and live regions, 8) Hiding decorative content, 9) Testing with screen readers (NVDA, VoiceOver), 10) Common pitfalls. Provide code examples and best practices.