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.
If you find one really awesome book or journal that fits your topic perfectly, try looking in the works cited/bibliography/reference list at the end of it. This should contain many more books and journals that are about your topic as well.
Although you may be limited by specific classroom or work related guidelines, choosing your topic is the first and most important step in your research paper project. Regardless of whether your topic can be anything you want or has rigid requirements, it is important to keep a few questions in mind: Is there enough research available on this topic? Is the topic new and unique enough that I can offer fresh opinions? Is it pertinent to my class/occupation?
The thesis statement is a 1-2 sentence statement at the beginning of your paper that states the main goal or argument of your paper. Although you can alter the wording of your thesis statement for the final draft later, coming up with the main goal of your essay must be done in the beginning. All of your body paragraphs and information will revolve around your thesis, so make sure that you are clear on what your thesis is.