I am a little late to this conversation, but here is my offering anyway. I whole-heartedly endorse the earlier link to social-engineer.org This is a great site with many great resources. I also suggest the following books:
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.

Good points Solinus. I was recently called for jury duty. This is an awesome place for people watching as there's not only a strong mix of people in the jury pool being from a cross-section of society, but it's also interesting to see professionals, lawyers and accused in the same environment.

It's fun to pick out a person and see if you can figure out what they do for a living, their background, etc. Then go talk to them and see if you're right.

It even made jury duty fun. Go figure.

Don