Mobile-first indexing has significant implications for blog SEO. Mobile-first indexing means that search engines will prioritize the mobile version of a website when indexing and ranking content. This means that blogs must be optimized for mobile devices, with a fast loading speed and a responsive design. Additionally, content should be optimized for shorter queries, as mobile users are more likely to use shorter searches. Finally, blogs should use structured data to make content easier for search engines to understand and index.