Distinguish arguable from non-arguable statements. A debatable thesis statement expresses an opinion. If you state, "More companies should administer drug tests to their employees," you have an arguable statement. In contrast, if you state, "More and more companies are administering drug tests to their employees," you have nothing to debate once you check the facts about the number of companies requiring drug tests. Some reasonable people in your writing audience must object to your thesis; otherwise the claim creates no debate.
Decide which type of claim you will argue. If your claim (thesis) predicts a future event, you may argue a claim of fact: Drought will become the No. 1 global issue in the next 10 years. If you argue that reality television harms society, you have a claim of value. A debatable cause-effect claim might list greed and speculation as the primary causes of gasoline price fluctuation. Frequently, debatable topics focus on government policies and solutions; e.g., the HPV vaccine should be mandatory for sixth-grade girls in Indiana.
Recognize words that create a debate. In the examples above, the word "will" may indicate a prediction, a claim of fact. In a debate about value, words such as "benefit" or "harm" can indicate the direction of the argument. In a cause-effect claim, arguing for the primary or most significant causes or effects can stage the debate. Clearly, the words "should" and "must" indicate claims of policy.
Narrow or broaden the scope of the thesis statement. Vanderbilt University suggests adjusting the scope of the thesis statement to fit the length of the assignment. For example, the broad topic "Positive Values of Talk Shows" would cover far too much information for a 10-page essay. If, however, you focused on the positive impact that Oprah Winfrey's talk show had on American culture, you could argue effectively for its value.
Create a thesis statement that previews your topic. If you simply argue that the United States should invest in more nuclear plants, you are omitting a preview of your reasons. If you add a brief preview of reasons -- less pollution, lower cost and efficiency -- the structure of the argument emerges. The statement might become: "The United States should invest in more nuclear power plants because they create little pollution, lower our energy costs and generate significant energy."