Your thesis should express the main idea of your paper without listing all of your reasons or outline your entire paper. It should be a simple statement, rather than a list of support; that’s what the rest of your paper is for!
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.
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.
An outline will help you organize your thoughts before you dig into the writing process. Once you’ve developed your thesis statement, think about the main points you’ll need to present to support that statement. Those main points are your sub-headings. Now, organize your thoughts and information under each sub-heading.