It's important to know some of the words in their local languages, as vegan and vegetarian are different in different languages. Also, what are your diet preferences, how do you pronounce no chicken, no eggs should be known to you and be sure about the ingredients they are adding into your meal. So keep your list of words handy as it would be easy to explain and get the right meal. For ex: Chicken is called Poulet in many European countries.
Keeping a backup for an emergency is always a good idea as being hungry ruins every trip, so keep your snacks ready, protein powder, energy Bars, dried fruit, nuts and travel-friendly packets of food, can keep you satiated when your options are limited or nonexistent.
Booking right hotels, tours and cruises will save a lot of your time in finding the right restaurant, as there are many hotels and tours, which customize and especially prepare vegan and vegetarian meals for their guests and informing them in advance ease all your worries. As it gets a big task to go out of your hotel and look for restaurants to serve you the right kind of food.