Start with simple questions first when shooting starts. This is to warm up the subject. It’s to make the subject feel at ease, so that you could move on to something deeper, to issues the subject would not normally talk about. If the subject feels like elaborating on a certain subject, don’t restrict him. You want to show the subject that whatever he says is important. If you make him feel important, you can expect to get some valuable information that the subject would not normally reveal.
As far as possible avoid referring to your list of questions you have prepared in advance. Go with the flow of the interview and follow where the subject is taking you on a certain theme. Only refer to your questions when you are lost as to what to ask next.
On finishing your interview, ask the interview subject if you have left out anything important. This will make the subject feel important and with a little luck you may get some useful information that you never anticipated in the first place.
In a nutshell, try to look from the viewpoint of the interview subject while serving your own needs. The more the subject is made to feel comfortable and important, the more successful your video interview will be.