Consider the source. This is one of the most salient phrases in all of journalism, but it can be applied to any kind of research. You want your source to be objective, above all, and the website from which you gather information should reflect that. Personal blogs, commercial websites (at times) and sites pressing any type of agenda are not objective, and any facts gleaned from them may be called into question. Focus your search on sites built by government and academic agencies. These bodies are more highly motivated to provide accurate copy and reliable facts since their reputations depend upon being seen as highly knowledgeable on a topic.
Determine whether the site is written in a well-organized and readable manner. This indicates that the author spent a great deal of time working on the site, and that same effort may also have been expended during their research and writing. Beware of sites riddled with grammatical and spelling errors as well as those that are poorly organized and difficult to follow. Although not all subject experts can claim to be writers, the fact that they did not take the time to correct mistakes indicates the possibility that they are sloppy in other areas of their working life, such as research and fact-checking.
Research the author. While the main source of the article may be a particular institution or company, it does not hurt to do a little fact-checking on the person who wrote it as well. He should have years of experience on the topic, and should possess relevant degrees, licenses or certifications in the area of expertise he's writing about.