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.
An easy way to develop your thesis is to make it into a question that your essay will answer. What is the primary question or hypothesis that you are going to go about proving in your paper? For example, your thesis question might be “how does cultural acceptance change the success of treatment for mental illness?” This can then determine what your thesis is - whatever your answer to the question is, is your thesis statement.
Support every statement you make with evidence. Because this is a research paper, there shouldn’t be any remarks that you make that cannot be supported by facts directly from your research. Supply ample explanations for your research. The opposite of stating opinions without facts is stating facts with no commentary. Although you certainly want to present plenty of evidence, make sure that your paper is uniquely your own by adding commentary in whenever possible.
Once you’ve gathered all your research, print it out (if it is an online source) and gather post-its or anything you need to mark notes in the books/magazines you are using. This step is very important: read through your research, take notes on what you think is important, and highlight key facts and phrases. Write directly on copies you’ve made, or use slips of paper tucked into pages to mark places of importance.