Have the subject step further away from the backdrop. I see it over and over and over again. Subject's too close. It picks up the wrinkles in the fabric, or the paper, or whatever. It tosses shadows on the backdrop.
You can eliminate most of these issues by simply having the subject take four more steps than where you would normally put them. If they seem close to the backdrop, they are. Move 'em away from there. Get them in a free space, away from the backdrop.