A website is effective if it provides the right information to the right audience. User interface is definitely important, but should not be too flashy. People do not visit websites to enjoy user interfaces. They look for information or solutions to their problems.
1) Effective Message (Content) : An effective website is the one which has solid, useful and note-worthy content. People come to your website to solve their own problems. Your website needs to have the content that at least helps them a bit. Say you are searching for information on “D.I.Y. plumbing”. Would you like to visit a site which claims to solve your plumbing problems, but actually provides nothing useful or insightful ? I would not.
2) Effective Design : A good design is one that pleases the eye and creates good first impression. And Effective design is one that helps in carrying the message across and is not obtrusive. In other words, it does not distract rather it engages. It offers them easy ways to navigate or find the content they are looking for.
3) Availability : A website is no good if it is not available at all times. Make sure you invest in a good web-host. You never know when potential clients will visit your website.
4) Searchability : Make sure your website is easily findable. Though there are lot of factors that make your website searchable, good content is one of the most important factors. If your content is good, your readers themselves will spread the word, share links etc and bring in more traffic.