Take a trip to your local library or university library. Although it may seem old fashioned, libraries are chock full of helpful research materials from books to newspapers and magazines to journals. Don’t be afraid to ask the librarian for help either - they are trained in research and know where everything about your topic is located.
Any information that doesn’t fit within the framework of your outline, and doesn’t directly support your thesis statement, no matter how interesting, doesn’t belong in your research paper. Keep your focus narrow and avoid the kitchen sink approach. (You know, the one where you throw in every bit of interesting research you uncovered, including the fungal growth in the U-joint of your kitchen sink?) Everything you learn may be fascinating, but not all of it is going to be relevant to your paper.
Although it may seem counter-intuitive, writing your introduction first may be more difficult to accomplish than starting with the meat of your paper. Starting by writing the main points (focusing on supporting your thesis) allows you to slightly change and manipulate your ideas and commentary.
Whenever possible, look for peer-reviewed empirical research. These are articles or books written by experts in your field of interest, whose work has been read and vouched for by other experts in the same field. These can be found in scientific journals or via an online search.