The document discusses 12 important technical SEO issues that were discovered in recent consulting projects. These include thin or duplicate content on internal pages, poor internal linking architecture, indexed staging servers, canonicalization issues, soft 404 errors, blocked crawler access, excessive redirects, unstripped HTML injection, and ensuring user-generated content is optimized. The document encourages checking for these issues and properly configuring content, links, servers, and user inputs to improve a site's technical SEO.