Opinions vary greatly among sound engineers on the best method and equipment for recording audio with a DSLR. You've likely seen many videos that use a lavalier microphone — the small piece that clips below the collar of the talent's shirt. Lavaliers come in both wired and wireless options. However, lavaliers can be a bit obtrusive both for the talent (who has to have a wire threaded down his or her shirt) and for the viewer (who has to see a microphone for the whole video).
When it comes time to shoot, clear out unnecessary people from the room and turn off the overhead lights. With your three-point lighting setup, there will be no need for those harsh fluorescents. When — and only when — everything is set up, call in your talent. There's nothing worse than being nervous, and then having to anxiously watch as lights are turned on and the camera is tested.