Popular website focus in the domain content they want their audiences to read and acquire information they need. Your domain must be related to your content. If you domain is car.com never mix the topic about bags because this will confuse your visitors.
If you are selling realestate never mix your content about medicine. If you are selling computers online never mix a content or images about watches. Be specific and direct to the point. Simple and elegant website are very clear what their website is all about.
For example if you visit the embed.ly they just focus about embedding scripts in your website. Most of the popular website create a high quality overview video what their website is all about. This will give a clear mental picture to your visitors and save time. Your website must be specifically define what is all about and how it can give benefits to your repeated visitors.
We want repeated visitors to get more traffic in our website.
Note: Your domain must be related to your contents.