A good thesis makes an assertion which is defendable over the course of a well-structured essay.
A thesis should not merely point out the obvious or seek to re-tell the narrative. It should look deeper into Shakespeare's craft or how parts of the play might be perceived and interpreted in a modern context.
Here are some sample thesis statements for essays about Fahrenheit 451:
In Fahrenheit 451, book burning, technology, and conformity are all sources of negative power.
In Fahrenheit 451, characters are unable to be content with life due to a lack of real experiences and a devotion to technology.
Notice how each of these sentences provides a structure of argument which would be followed in the rest of the paper.
Be ORIGINAL in your thesis statements, and be sure you could defend your thesis with textual evidence.
Thanks to Ms. Athearn for the sample thesis statements!