The Table of Contents should tell a story. The title of each chapter should be rich in information without being cluttered. Now obviously those two imperatives are contradictory (potentially). A spare, uncluttered title might not have enough information, and adding information to it might make it cluttered. Where the table of contents is most important is on the grant proposal or book proposal, when you are approaching a funding agency or book publisher. In other words, when the book itself is not there.
Information is also somewhat at odds with cleverness, or with phrases that are suggestive but not informative. Many people use quotations as part of the title of a chapter, but this does not work as well if the meaning of the quote or phrase is not transparent without extra explanation.
I craft and recraft my table of contents constantly. Not just every title, individually, but the entire list. I want to make sure that each title is adequate, but also that the titles balance nicely with one another, without repeating the exact same format, and are equally informative.
Here is an old and new table of contents for more or less the same project:
Chapter 1: Modernity and its Discontents
Chapter 2: Spanish Modernism and the Paradoxes of Literary History
Chapter 3: Contemporary Spanish Poetry: Late Modernism and the Cutlural Logic of Anachronism
Chapter 4: Alternate Models: Machado, Jiménez, Cernuda
Chapter 5: Play and Theory of Lorca's Duende: Nation and Performance
Appendix: Glossary of the Duende
1. The Grain of the Voice: Nation and Performance in Lorca’s “Juego y teoría del duende”
2. Jorge Guillén, Luis Cernuda, and the Vicissitudes of Spanish Modernism
3. María Zambrano and the Genealogy of Late Modernism
4. Fragments of a Late Modernity: Samuel Beckett and José Ángel Valente•*
5 Antonio Gamoneda and the Persistence of Memory
6. What Claudio Knew
7. The Spanish American Connection: Blanca Varela and Eduardo Milán
8. Poetry and Aphorism (From Antonio Machado to Luis Feria)
9. The Verse Paragraph (From Juan Ramón Jiménez to Olvido García Valdés)
I'm still not happy with the table of contents. #6 needs to be more information-rich.