Use a focal length of 70mm plus to get good flattering images of faces
Don't chop of fingers or hands.
Shoot faces with a little of neck. If you want to include shoulders then best is to go down upto the waist and try to get hands in the frame. Don't chop hands or fingers off. Ask folks to put there hands somewhere above the waist. It may feel fake but will look more natural in the photo.
Focus on people's eyes and if you want to recompose then keep the shutter pressed halfway so that the focus does not change and move the camera around to compose what you want to be in the photo