Let the assistant taste the Bagels first, they might be left over from the previous day's shoot.
If no one will deliver food to the studio, don't go outside alone.
Don't ask the photographer for the RAW files, it tends to make him cranky.
Don't ask the photographer how many Megapixels his camera has, the answer will put you to sleep.
Don't ask the models for a date, they are young enough to be your children.
Don't offer to help, the Photographer will make you lift something heavy.
If the Photographer offers to detail your car during the shoot, you're paying him way too much.
If there is a pay phone in the studio, it's a bad sign.
Wear good shoes and bring a jacket, the studio floor is always cold.