Check out this Website Credibility report from Stanford University.  The compiled 10 guidelines for building and improving the credibility of a web site. The guidelines were based on three years of research that included over 4,500 people.

Here is a sample:

Make it easy to verify the accuracy of the information on your site
You can build web site credibility by providing third-party support (citations, references, source material) for information you present, especially if you link to this evidence. Even if people don’t follow these links, you’ve shown confidence in your material.

Show that there’s a real organization behind your site
Showing that your web site is for a legitimate organization will boost the site’s credibility. The easiest way to do this is by listing a physical address. Other features can also help, such as posting a photo of your offices or listing a membership with the chamber of commerce.

Highlight the expertise in your organization and in the content and services you provide
Do you have experts on your team? Are your contributors or service providers authorities? Be sure to give their credentials. Are you affiliated with a respected organization? Make that clear. Conversely, don’t link to outside sites that are not credible. Your site becomes less credible by association.

Read all to Web Site Credability elements.