I think that everybody should read How to Win Friends and Influence People by Dale Carnegie.
Especially Muslims... in particular, those Muslims who want to give da'wah. The best of people who called to Islam didn't need a book like this--and if we follow his example (saws) then we wouldn't need it either. But it's my view at least that this book can help people (like us) understand better ways of dealing with other people.
Even though its title, How to Win Friends, sounds sinister and deceitful, like you're trying to get something out of another person, the book seems to me more about good manners and etiquette than sales. (And I do hate to compare da'wah to sales.)
You see, one problem the Muslims seem to have today is that they tend to offend and arouse resentment in other people whenever they talk about Islam. Maybe they are berating in public (rule: always let the other person save face,) or shouting "Haraam, Haraam!" (rule: don't criticize) , or never owning up to their mistakes (rule: admit your wrongs quickly & emphatically.)
So I see the book as being incredibly useful in trying to deal with other Muslims and non-Muslims. And I mean useful when organizing events, on committees, in dialogues or debates, when trying to encourage someone to adopt a religious practice (e.g., prayer, hijab), or abandon something that is forbidden (e.g., alcohol, interest), and not just in standard da'wah.
Some of the tips in the book (you can view a summarized list of them here: Summary) struck me as being especially relevant in giving da'wah, so I want to post about them. One brother I know even recommended this book as part of a da'wah training program, at the first or second level, as he thought it was important enough for anyone calling to Islam to understand these techniques in dealing with people.