Look for clean, odorless conditions. Bad smells mean bad sanitation. Can your pet get exercise and personal interaction. Bring your own food from home, especially if your pet is a finicky eater. Tell them your regular feeding schedule.
Most kennels feed once or twice a day and pick up the food shortly after feeding.
Milo, on the other hand, will eat anything, anywhere, anytime. Provide any necessary vitamins or medications, with clear instructions. Bring a familiar plaything. It shouldn't be something that will get dirty. Don't forget to tell them how to reach you as well as someone who will be your local contact.