when unwrapping, using the project from view option can be usefull. Also once you've unwrapped and are working with the layout, use pins to fix the position of the basic outline and unwrap again to redistribute the inner vertices within the fixed shape to reduce stretching. weld, align x and align y are helpfull as well, press w in the uv image window.
heads can be tough to get a layout that is both easy to paint in 2d and minimizes stretch. even more so to layout for a photo texture and still minimize stretch.
you may try doing a simple unwrap without alot of editing to the layout, you will have no stretching but will get some tough flow to work with, so use texture paint in 3d to block out areas and kind of 'map out' the 2d locations. You really won't be able to use a photo as is but need to do some editing: copy rotate and blend as defined by your blockouts to get it to fit your layout.