Get close. Metaphorically and actually. Be nice. Respect your subject. Collaborate. Don't dick around with all the controls on your camera and your lights. Be ready to photograph when it's time to photograph. Nothing ruins the flow of a portrait shoot worse than the photographer diving into the menu to sort stuff out. Waste of everyone's time. If your work doesn't flow then you are not "working" on a project, you are just playing around with your toys...
Must be Monday. I'm in
that kind of mood.