One such short work is Fr. Paul O'Sullivan's The Divine Office: How to Say it Devoutly; How to Make it a Pleasure. This short work focuses on why we say the Breviary, and how we can simply make it a pleasure as well as the liturgical function it is.
Three other books which may be found similarly useful are:
- first, the Rubrics of the Roman Breviary and Missal are essential if you have a Latin-only Breviary (FSSP, $10);
- secondly Fr Bernard Hausmann's Learning the new Breviary (PCP Books, $14) is good for when you still can't work out what the rubrics mean; and
- thirdly, Fr E.J. Quigley's The Divine Office -- although written in 1920 (and thus applicable to the 1911 Breviary), this book has a whole section on the "moral and ascetic theology for the recitation of the Breviary". It is available online at Project Gutenberg, but you can likely get cheap reprints on Abe Books.