Why keep it simple you ask? You wan't to attract the masses. Emulate what works and sells. Vogue is a great example.
Take it easy on the concepts and ideas when shooting for your portfolio. There is a fine line between couture and corny. It takes the right model, lighting, styling, and photographer to pull it off. Don't get caught up in overly made up faces and kooky ideas with newbies. These tests will not land you a paying job.
I'm not saying you shouldn't be creative and have fun. Showing off your flair has a place here and there to keep your book interesting, but clean simple beauty should be your first and primary focus.
It's worked for me and countless other professional makeup artists. I guarantee it will work for you. Mary RC