Your thesis statement should be cogent and coherent. Dictionary.com defines "cogent" as a relevant point that is convincing or believable by virtue of forcible, clear, or incisive wording. It defines "coherent" as ideas that are logically connected, consistent, and harmonious.

The thesis statement should also pass the "blank paper test." In other words, you should be able to print off just your thesis statement on a blank piece of paper and show it to people. Based solely on that once sentence, everyone should know precisely what the paper's overall topic of discussion is about and where you stand on the issue.

If your argument paper is long, you may want to forecast how you will support your thesis by outlining the structure of your paper, the sources you will consider, and the opposition to your position. Your forecast could read something like this:

First, I will define key terms for my argument, and then I will provide some background of the situation. Next I will outline the important positions of the argument and explain why I support one of these positions. Lastly, I will consider opposing positions and discuss why these positions are outdated. I will conclude with some ideas for taking action and possible directions for future research.

This is a very general example, but by adding some details on your specific topic, this forecast will effectively outline the structure of your paper so your readers can more easily follow your ideas.