Over the years I have tried on many hats the film industry has to offer. Sometimes filling the small but ever necessary stand-in slot. Other days were spent with a handler hustling me between hair and makeup and wardrobe trailers in the hopes of not falling behind on the day. No matter how significant,or often insignificant, the position was always defined. There were clear lines drawn between talent and crew, principal and background, above the line or below the line jobs. There always were until the day I became a photo double.
A photo double's job is to take pressure off the lead actor. Any time the shot can be done without the star being there, the double subs in. Sometimes it's a simple over the shoulder shot, other times it's unloading a vehicle or walking down stairs. The less time the star has to be present the better, but the tricky part is figuring out where the boundaries are. No one teaches you how to photo double. Stunt double, yes. Body double, yes. But photo doubling is different every day on every show.
Some things you can do:
Watch the show. If you are on a TV show, instead of a film, watch some episodes. Get a feel for the pace, your actor, and the characters you will be interacting with. You don't need to be up to date, but you should have an idea of the plot. This will take off a lot of pressure your first day on set.
Introduce yourself to the crew. You are 90% one of them and they should accept you. They will help you do the best job by getting you pages, call sheets, and a chair in video village.
Be ready to interact with all the principal actors. You will likely act on camera with all of them. If you are on the same show long enough, you will get to know them well. This is not a background job.
Most importantly, pay attention to everything your actor does. You are there to be her when she is not. You and her stand-in will work together to make it appear like the star of the show is there. Be familiar with the scenes, note all of her marks, movements, and gestures as you will repeat them. Although you will not likely read the lines aloud (because they would have to pay you more) don't miss the opportunity if they change their minds.
Some days you will be treated like royalty with parking privileges, a trailer, and endless meals and manicures. Other times you will be in a folding chair on an empty sound stage with nothing to do for twelve hours. Just remember, be prepared, be professional, and you can have a steady, challenging job in an otherwise chaotic industry.