Paul Miller's A Praying Life is as good a book on prayer as I have read in a long time. Firstly, it is an easy and practical read, full of honesty and is not scared of dealing with difficult questions. It acknowledges straight off how glibly we say "I'll pray" and then either forget or become guilt-ridden at our lack of dedication or competence.
The praying life, he says, should feel like dinner with good friends. Miller has a particular take on prayer gleaned from his genuine experience, biblical knowledge but also through the things he has learnt through being father to his mute and autistic daughter Kim. He movingly tells stories of his own communication with his daughter and hers with him and shares the insights this has given him into how and why we pray. The book is packed with wonderful stories and grace-filled help and I cannot commend this highly enough if you want to cultivate a praying life.