1. Offer it whenever you possibly can. Make your offer specific ("We'd be glad to host you for two nights, but we already have plans to be away during the dinner hour on Thursday").
2. Do not ask for it from anyone to whom you are not related or very, very close* if you have more than three children. Yes, we need it the most, but we are also terribly burdensome to house and feed (more than we realize, because we're used to the crying, chaos, and vanishing gallons of milk). It is an imposition for us to ask. The Lord will provide one way or another, whether through a kind person's unexpected offer (see #1), a change of plans, a surge of resourcefulness, a surprise bonus, a humble submission to reality, or some other means. This is one of the crosses we must bear, and far from the heaviest if you ask me.
3. Do not drop by "just passing through" with a van full of kids at mealtime. Do not stay so long that a planned one-meal visit turns into a two-meal visit. Do not put a host on the spot. "Maybe they'll invite us in" is never an acceptable meal plan.
4. If there is someone whom you'd like to see while you are traveling, invite them to a picnic or a restaurant meal with your family, compliments of your house.
5. If the hand of hospitality is extended to your family, it is fitting for the value of your hostess gift to correspond to the size of your family (unless your host's family is larger).
*I offer myself as an example of a person who does not consider herself very, very close to anyone whom she only knows via the Internet, even though we're all identical soul mates. No hard feelings, cherished readers. ;)