In practice
Work through it in order of leverage: intent match first, then title and headings, then internal links, then markup.
Audit by template rather than page by page — most on-page issues repeat across thousands of URLs.
Why it matters
It is the part of SEO fully within your control, unlike links or algorithm changes.
Done properly it is also the cheapest: no new content, no outreach, just the pages you already have.
Related terms