How to create successful sites? This is a very good question. I will try to outline a few answers.
Many people measure success using very different parameters. To keep this article focused, I will concentrate only on business websites. For a business website, the most important parameters are traffic and its level of conversion.
Is very important to drive visitors to your site, if no one or very few people go to your site, you can't be successful. It's like a store without clients. In order to become successful, the first step is to attract people to your site, most important is that you need to attract people interested in what you offer (quality traffic).
How to get traffic
There are two complementing approaches:
Natural search engine traffic and Advertising campaigns.
Level of conversion
This is the percentage of your site visitors that buy or execute an action on your site. The level of conversion principally depends on what you offer, it can be products, good price, service, content, functionality, etc.
Your site success is determined by the traffic it receives and the effectiveness of your selling process. If your offer is attractive and you are able to drive quality traffic to your site, a higher conversion ratio can be achieved.