This book deals specifically with private prayer - not public or family-level prayer - done indoors or outdoors in a chosen place: a nook, a field or another place in nature, whatever alone-place one might choose.
It's not a book that seems to shine at first. It may feel like something done before if one has read books on prayer.
But the Puritan flavor and the deep reasonings and answers convince quite well of the excellence of this form of prayer, and give deep reasons why one should strive persistently to keep it, even if one has a lot to do (sometimes even cutting a moment of time from eating or sleeping, though it's clear it's not really *all* of those times). Brooks guides one well on how to do it (and what one's state of mind and emotions should be like; he also suggests keeping a prayer diary to record how things go) and gives solid answers to questions included.
So, even if you've read books on prayer before, this might bring some more motivation and guidance to doing it in its private form. And private prayer is essential for one's connection to God, for all Christians. Recommended. :)