Inside Out by Maria v. Snyder

Trella is a scrub, one of the thousands who work in the lower levels, keeping Inside clean for the Uppers. The rules for staying alive are;

1. Keep you head down

2. Don't get noticed

Trella breaks both these rules, and accidentally starts a rebellion.

Inside Out examines the dystopian society, where only the rich are happy. It was well written, and a very good book.