While conducting research on the web, it is imperative to evaluate the website in question for authority, documentation, currency, and bias. Doing so will ensure that you are using the most credible information possible to support your thesis.
Authority and Accuracy
Who produced the site? Are they a credible source? What is the purpose of the site? Why was it created? Is the person, organization, or group qualified to write this content? What is the domain of the URL?
Documentation
Is there adequate documentation for factual statements? Is the documentation reliable, verifiable from a second source? Is there enough information to cite this information in a paper (author, title, source, date)?
Currency
Is the information up to date? When was it created, or last edited? Are the links up to date or dead? Is the author using outdated statistics?
Objectivity and Bias
Is the document biased or slanted? Are there few or no logical errors such as appeal to authority or circular reasoning? If you found this information a printed source, would you trust it?
One of the most powerful web search strategies is called "site limiting." This entails limiting your search results to either a specific web site, or top-level domain (i.e. org, edu, gov). The result is a more focused set of results, allowing you to evaluate and select sites within in a narrower context. Below is a comparison of a general topic search using Google and then a more focused search of the same topic, limited by domain (all results restricted to the .gov domain). Notice the difference in the amount of results retrieved --give it a try with your research topic!