Nothing to worry about. You'll be greeted warmly and become like a family member in no time.
I'd just keep in mind that Mexicans are, in general, some of the most courteous people around. Always use greetings such as "Buenos Dias, Buenas Tarde," etc. Always say "gracias," "con permiso," and "por favor." When you feel comfortable, use more informal greetings such as "¿Que tal?" or even ¿Que honda?"
One way to start a conversation (maybe in a few days) is to ask to help out in the kitchen. Then begin a conversation about cooking and food - one of the favorite topics in Mexico, believe me. Arrange, also, as soon as possible, a trip to the central market. Be inquisitive about any food items you see there that are unfamiliar. Ask about them. (Also, it's OK and even welcomed to ask for a sample, say, of cheese, ice cream, or even of carne asada.)
La Clima is always a good topic, especially in the central mountains of Mexico, which has an almost ideal climate and weather.
Google information about Cuernavaca before you go. Share any interesting facts with your hosts. (Its name, itself, is fascinating.)