1. Have I taken a position that others might challenge or oppose? If your thesis simply states facts that no one would, or even could, disagree with, it's possible that you are simply providing a summary, rather than making an argument.
2. Is my thesis statement specific enough? Thesis statements that are too vague often do not have a strong argument. If your thesis contains words like "good" or "successful," see if you could be more specific: why is something "good"; what specifically makes something "successful"?
3. Does my thesis pass the "So what?" test? If a reader's first response is, "So what?" then you need to clarify, to forge a relationship, or to connect to a larger issue.
4. Does my essay support my thesis specifically and without wandering? If your thesis and the body of your essay do not seem to go together, one of them has to change. It's o.k. to change your working thesis to reflect things you have figured out in the course of writing your paper. Remember, always reassess and revise your writing as necessary.
5. Does my thesis pass the "how and why?" test? If a reader's first response is "how?" or "why?" your thesis may be too open-ended and lack guidance for the reader. See what you can add to give the reader a better take on your position right from the beginning.