Kevin Mitnick - Art of Deception, Art of Intrusion and his latest Ghost in The Wires. These are great books with real valuable examples.
And Social Engineering - The Art of Human Hacking by Christopher Hadnagy this is a new book and has very good reviews. I have read it myself and found it to be one of the best. It gives a very solid methodology to performing Social Engineering. I believe it it the first time a methodology has actually been laid out for Social Engineering.
Then I would suggest that you just spend a lot of time observing. Retail stores and malls are great learning environments. If you can set yourself up where you can here people on phone conversations you will find a wealth of data to study. Take notes as you observe them. I try to find business people in a food court that are on their cell phones, I sit next to them and listen to their end of the conversation. Is it a sales call? A meeting? what are his mannerisms while he is speaking? Is he eliciting information?
The world is the best place to go to learn how to deal with people.
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