This is probably the best book I've read on the topic of spiritual warfare.  The book is based on scripture.  Spurgeon discusses extensively the fact that we can defeat Satan through the power of the gospel.  His writings are practical and he directs his focus to where he found Satan at work in the lives of people - enslaving them in sin, keeping them from the influence of the gospel, hindering their spiritual development, bringing discouragement, depression, and moral failure.