Tim Ferris makes his living doing it, in the four hour chef you will learn DiSSS & CaFE that teaches how he does his work which will answer your question.
If your looking for more online course.
Try Ramit Sethi's How to talk to anybody or Instant+Network.
As with any successful relationship, it's starts with creating a value or usefulness to the other-side. The two above will help you with that....
