Be the first to order. That way you won’t be tempted to go along when the rest of the gang orders more than you’d like to eat.
Consider à la carte. Try getting a soup or salad and an appetizer, or a couple of side dishes, instead of an overly large entree. Many restaurants these days offer smaller “tasting” plates or tapas-size portions too. They are worth a try and often just right in size.
Split the difference. If an entrée sounds like too much food, see if one of your dining companions would like to share it with you. Or set aside half of the food as soon as it arrives and ask the waiter to wrap it up for you.
Ask for sauces and dressings on the side. Most restaurants use a heavy hand with toppings. When they’re on the side you can control the amount without having to miss out. Rather than pouring them on, dip the tip of your fork into the dressing or sauce, then take a bite of food, so you’ll get a little taste in every bite.
Ask questions. Request that food be prepared your way, within reason (there’s absolutely nothing wrong with requesting a salad on the side instead of fries). Ask politely but unapologetically; remember, restaurants are in the service business. Most are more than willing to accommodate your request.