I personally use both Google and Wikipedia (both often overlooked) as a tool from which I can do further research. While I wouldn't want to cite either as a source, or rely 100% on either, they can both be giant stepping platforms from which you can be lead to credible sources and citations!
Family Tree has a wonderful article on doing this here. With the advent of the Internet, and the thousands of articles and books and documents added daily, you'll want to check often! But, as I said, I'd use that as a stepping stone only.
Once you are taken to the link for anything that comes up in the giant search engine, then begin to actually research and prove that the mention is legitimate. You never know just what you may find of value!