If you have an interest in photographic portraiture, whether you've known it or not, you will probably be familiar with the work of Gregory Heisler. Among other achievements he has 69 Time Magazine covers to his name. He became renown in 1991 for the stunning in-camera double exposure of George HW Bush (above) for the cover of Time Magazine, a shot which caused him to loose his White House photographer privileges, in my opinion it was probably worth it.
I've recently stumbled across a series of YouTube videos produced by Profoto USA where Heiser explains the methodology behind some of his most iconic shots. From the videos Heisler appears to be incredibly relaxed even laid-back. But that obviously doesn't mean he's relaxed about his work, in his preparation he's incredibly meticulous. It's fascinating to see the level of planning and experimentation that goes into each of these shots.
Whatever your level of experience you're going to gain something from watching these videos even if it's just respect for this master of his art.