1. Keep in mind that some restaurants don’t allow modifications. If that bothers you, keep in mind that there are plenty of restaurants that do allow them, and you will probably be happier patronizing those establishments rather than stewing in a restaurant that you feel is not accommodating you.
2. And some dishes cannot be modified in the way you want them; if the steak has been marinated in an oil that contains garlic, it is impossible to alter that dish to accommodate a garlic allergy.
3. Speaking of allergies– don’t characterize an aversion to something as allergic to it. Calling something an Allergy sets off an array of protocols that stop the kitchen in their tracks. Grills and tongs may need to be washed in the moment, gloves donned, fresh plates brought from another part of the restaurant to prevent cross contamination. This delays service for every party in the restaurant, including yours. If you have set off all these protocols to accommodate your “gluten allergy” that is truly only a desire to avoid eating carbohydrates, don’t be surprised if every staff member in the dining room stares daggers in your direction when you order the banana cream pie for dessert with the excuse that “a little gluten is ok, I’m not that allergic.”
4. Be polite. Politeness goes a long way. Not that you won’t be helped if you are not polite, but it can make a difference in how hard the server negotiates on your behalf with the chef. In the heat of a service, a server may know that she only has three serious favors a shift to ask of the kitchen. She’s not going to go toe to toe with the sous-chef for a guest that was rude; she’ll take his initial ‘no’ and be happy for it.