Some popular Ugandan websites include yaaka.cc, monitor.co.ug, jumia.ug, newvision.co.ug, and smart24tv.co.ug. Websites become popular due to search engine optimization, which is the process of improving website traffic and rankings by optimizing on-page elements like keywords, headings, and links, and off-page elements like link popularity and forum posting. Key aspects of on-page SEO include using keyword-rich headings, tags, multimedia, and linking both within and outside the site.