On-Page SEO is the set of optimizations made directly on the site's pages to improve search engine rankings. It includes: page title (title tag), meta description, headings (H1, H2, H3), body content, images (alt text), URLs and internal links.
The fundamental On-Page SEO best practices are: use the main keyword in the title and H1, write meta descriptions that encourage the click, structure the content with a clear heading hierarchy, include relevant internal links and make sure URLs are descriptive and short.
A common mistake is focusing only on keywords and forgetting the user experience. Google evaluates whether the content truly answers the search intent. If the user lands on the page and quickly bounces back to Google (pogo-sticking), that signals the content was not relevant, no matter how well optimized it was from a technical standpoint.