Decide whether your paper will analyze your topic, explain it in depth or take a stand and argue in its favor. Effective thesis papers do one of the three. Graduate students will have conducted their own research; at high school and college levels, it might be best to choose an angle for your topic based on the reference materials you have found, rather than coming up with a thesis and then trying to find information to support it. Read through your notes and bookmarked pages. Do you have enough material to break a topic into essential components for an analysis paper? Have you found varied sources that will explain something from a number of different angles? Do you have a strong feeling about what should or should not be done, and evidence to help you argue your point?
Find an interesting perspective as the focus of your paper. You might want to compare two seemingly different things or contrast two apparently similar things. Does any of the information you've gathered seem to correlate to something happening in the world today? A thesis for a literature or historical topic might compare current events with those recorded or created in the past. Think about "turning points" in your topic: a key historical moment, the climax of a plot or an important scientific discovery might be involved. Imagine if things had gone differently and what the implications might be. Your thesis might compare or contrast the past and present, fiction and reality or two sides of the same issue.
Summarize what you have decided to write about in a thesis statement. The thesis statement should be written as fact. For example, an analysis thesis might start with the statement: "A variety of factors led to ..." while an explanatory paper will convey, not in so many words: "The truth about ____ is ..." The statement for an argumentative paper may be easiest to state, although it may also be hardest to support. It will probably include a word such as "should" or "must," and it will say, in essence, "What I believe is this ..."
Your thesis statement should be a composite of elements, and a good number of elements is three. An analysis paper should note three factors, an explanatory paper should mention three key elements and an argumentative paper should give three reasons. These elements can become numbers 1, 2 and 3 in your outline. Delve deeper to figure out at least two ideas you want to use to support each of those three points; these will be the A and B under each point. You can expand on the outline if you must, but this format will get you started.
The thesis will begin with an introduction and end with a conclusion that restates the thesis and expands it a bit by weaving in information from the paper; in between is the body of your work. This format looks like: This is what I will say, Now I'm saying it and This is what I said. Each point within the outline will follow the same format: This is point number one; these are the two ways I justify or explain or argue for it (A and B); and this is what I just said (in summary).
Refer to your assignment for specifics; cite your sources in some standardized way and you might need to create a table of contents with page numbers, especially for a longer thesis. Always wait until the last step before you add page numbers to the table of contents, because page numbers can shift as you add and edit things. Present your thesis in the exact way described in the assignment.