On page optimization involves optimizing elements on a website like text, images, tags, structure, and internal links to help content rank higher in search engines and drive more traffic. It includes optimizing the title tag, meta description tag, robots.txt file, URLs, anchor text, images, H1 tags, and keywords to help search engines understand what the page is about and make the content more visible to searchers. Elements like headings, content, and internal linking are also important to on-page optimization.