On-page ranking factors are the elements that can be optimized within the website to improve its visibility in search engine results pages (SERPs). These factors help search engines understand the content of a webpage and how it is relevant to the user’s search query.

Here are some of the most important on-page ranking factors:

1. Content: The content of a webpage is the most important on-page ranking factor. The quality and relevance of the content on a webpage can determine its ranking in the SERPs.
2. Title tags: The title tag is an HTML tag that provides a brief description of a webpage's content. It is displayed in the SERPs as the blue clickable link. Title tags should be descriptive and concise, containing relevant keywords.
3. Meta description: The meta description is a short summary of a webpage's content that is displayed in the SERPs under the title tag. It should be well-written, informative, and include relevant keywords.
4. Header tags: Header tags (H1, H2, H3, etc.) are HTML tags that organize the content on a webpage. They should be used to structure the content and make it easy to read for both users and search engines.
5. Keyword density: Keyword density refers to the number of times a keyword appears on a webpage. It should be used naturally within the content and not overused to avoid being penalized by search engines.
6. Image optimization: Images should be optimized for both search engines and users. This can be achieved by using descriptive file names, alt tags, and captions.
7. Internal linking: Internal linking refers to linking to other pages on the same website. This can help search engines understand the structure of the website and improve the user experience.
8. Mobile-friendliness: With the increase in mobile internet usage, having a mobile-friendly website is crucial. It should be optimized for smaller screens, load quickly, and have easy-to-use navigation.
9. Page speed: Page speed is an important ranking factor as users are more likely to abandon a webpage that takes too long to load. It can be improved by optimizing images, reducing HTTP requests, and minimizing CSS and JavaScript files.
10. User engagement: User engagement is becoming an increasingly important ranking factor. Search engines use metrics like bounce rate, time on site, and click-through rate to determine the quality of a webpage.

In conclusion, on-page ranking factors are crucial for improving a webpage's visibility in search engine results in pages. By optimizing these factors, webmasters can improve the user experience and increase their website's traffic and rankings.