Always talk to them about their style of answering for the camera, because this is different than the way we speak in normal conversation. Tell them to always look at you instead of the camera, unless you are going for a more confrontational style. Make sure that they know they need to include the subject of the question in the answer they give. For example, if you were to ask them, “What is your favorite flavor of ice cream,” their answer should be, “My favorite flavor of ice cream is,” This will save you from having to use some kind of voice over in the final editing because each clip will make perfect sense on its own. Always sit only a couple feet in front of the subject because, even though they have a microphone on, they will feel like they need to raise their voice if you are too far away.