SEO for national company with only one locatio

Ok, so up until this point, I`ve only preformed local SEO for a few businesses in my town. I am now faced with an national company with only one location. They have no SEO implemented at all and are wanting to go with me! I couldn`t be more excited but I have no clue as to where to start for their national strategy. Does anyone have any pointers or tips that would be useful for me? Thank you!!