Unless you've visited Japan before, your Japanese host family will be your first contact with true Japanese culture. MAKE THE MOST OF IT!!!
Your host family will almost certainly go out of their way for you — as is the spirit of Japanese hospitality — to make you feel
at home and ensure you settle into your new life in Japan smoothly.
At least one person in each family speaks English, to some degree. If your Japanese is bordering on zero ability, like most JETs when they first arrive, bring a Japanese-English dictionary to the dinner table. It creates a lot of amusement, and they'll be impressed that you're trying to learn. Also remember that they're basically doing this because they want to meet you, and become freinds with you. Keep an open mind about your new environment, and you'll have a great time.
Most JETs stay with their host family from 2 weeks to a month, depending on how fast you are able to find an apartment. Many also stay in
contact with their host family after moving out; developing a close relationship with their host family that lasts the duration of their
stay in Nagoya.
Remember that many things you'll experience will be new, and much different from what you're used to in your home country. Also as far as food goes, unless you're allergic, try everything! You might find that things you never thought you'd eat become some of your new favorites. Above all, try to keep a sense of humor, and adventure, about this part of your experience. It's not just a unique opportunity to see first-hand how a Japanese family lives. It's a chance to participate (at least briefly) in their lives, and to let them participate in yours!