With gentleness, common sense and a touch of humour (things I don't necessarily associate with "how to" books on prayer!) John Pritchard gives an explanation of prayer, and guide to praying, as a Christian.
Ideal for somone who is new to faith, or returning to faith in mid life, but it also has some ideas and suggestions (especially in the later more advanced sections) which any Christian wanting to deepen their prayer life will find helpful.
Yes, it is a specifically Christian book, from a middle of the road Anglican perspective - but if that's what you are looking for do try this!