On the actual wedding day, the couple cannot actually look after the photographer therefore a responsible, assertive and calm minded person is ideal who knows their job and is not distracting. The photographer must handle all the photo details and logistics independently. The couple must build a friendly and comfortable rapport with the photographer because that will reflect in the photos.
Also the couple must meet the photographer in person and get to know if his/her skills are the type that suits them. Do not pick someone who relies on props too much instead choose someone who focuses on human expressions and emotions because that is what makes the photos beautiful.
The couple can have a pre wedding shoot to figure out the problems and few kinks in the photos. It also gives them an opportunity to relax and get to know the photographer more personally. The photographer can also be more creative and relaxed without the pressure from the family and in a less formal setting. It also gives the couple an opportunity to express their expectations and the photographer to understand what the clients actually want.