I am the master at interviewing people. The reason that this is my special talent is because I know that an interview is not some planned event with an agenda, you can't predict the direction the conversation will go because you do not know the answers. The purpose of the interview is to find the answers.
I have had the opportunity to mentor other investigators regarding the simplicity of the interview because it is simple. For example, last week I had to conduct a interview on the fly while the client sat in the background passing me notes. This interview had alot of different variables that could have made it a disaster but I was able to get the information I needed because I focused on my objective. I started out by introducing myself, I always ask permission to talk, I asked if this is a convienent time. This gives the person being interviewed impression that they call the shots. I make small talk and between questions about family or friends I ask questions related to the reason I called. Once a person is comfortable in conversation they are happy to talk. The key is to make them comfortable--make them feel like they are talking to a friend. At the same time I never mislead them, I am always honest about the purpose of my call.
Interviews are not a complex list of questions that follow a specific formula. The minute that you get caught in that trap the interview is doomed. Have some key words, specifics or date of importance as part of your notest before you start but never expect to follow a formula. Go with your gut and keep it simple.