A discourse by vipassana master Webu Sayadaw (1896-1977) which explains how to make the most of anapana meditation - observing the breath. The discourse takes the form of a dialogue with a disciple.
This booklet is a small gem, powerful in its simplicity. It inspired me to intensify my meditation practice and really make the effort of "lighting a fire" during meditation, instead of doing it half-heartedly. It's also somewhat humorous, because the disciple in the dialogue puts forth all kinds of objections he can think of to explain why he can't do what he is supposed to do. Webu Sayadaw explains how anapana meditation, which is usually seen as a concentration exercise, can be approached as a form of insight meditation.