Be useful. While you're staying with others, you are using their electricity, their water, their heat and more. Most hosts won't mind, but show them that you realize and appreciate their kindness and their inconvenience by contributing what you can. Whether it's money or just doing the dishes and making your bed, be sure to not only say thank you, but show your gratitude in meaningful ways. Better than doing the dishes or making your bed, why not offer to cook your hosts dinner or make their beds.
Show your hosts respect. While you are enjoying their hospitality, it's not a time to show your differences of opinion or habit. Save the controversial discussions and actions for some other time. If you see things headed down those paths, simply laugh, and say, "I'm so glad we're able to be such good friends and still have the differences that make life interesting." Then change the subject to more neutral ground.
Don't disrupt their lives. Adopt the schedule and the routine of the people who are nice enough to share their home with you. Sure, you can have fun on outings together, but be sure you don't ask them to put off important or routine things in their life to entertain or accommodate you. If your host gets up early, make sure you rise and shine with them. If they sleep late, don't make noise or commotion happen until they're ready to start their day. Likewise, if they have different sleep schedules, or if you know you'll be out late and past their bedtime, make sure you know how you can cause the least inconvenience or disturbance when you return.
Let everyone have their privacy. Just because you're visiting doesn’t' mean daily life and other personal relationships have changed. Be sure you spend at least one hour every day doing something on your own away from your host's home. If you sense that you or your host needs more than that, take the opportunity to find somewhere else to be for the day. Make sure you won't be needed or that others will have to spend time waiting for you while you're gone.
Try not to use things that aren't yours. Let your host know if you need something, but do so in a polite way that doesn't require more of them than they are already offering. Saying, "Can you tell me where I can buy this?" or, "Where can I go to do my laundry?" is a better way of allowing your host to offer without putting them on the spot to give something they cannot afford or do not want to share.
Clean your bathroom. No one likes to clean up the bathroom after others. You should definitely do this at least the day you leave, if not every couple of days in between. Keep your bathroom and toiletries in a bag in your room or suitcase between use. Otherwise, ask if there is a corner of the bathroom counter that you can use to keep your personal items, and keep it neat and clean.
Don't mess around with the heating or air conditioning settings while you're there. Putting on a sweater if you're cold or lighter clothing if you're warm is a simple way to avoid annoying temperature wars in the house while you're there. Let your host decide if they have enough room in their budget to alter the settings.
When you leave, be sure you leave behind a good impression and a hope that you'll return again. A simple gift of a flower and a hug with a big warm "thank you" is probably enough, but let your conscience and your pocketbook be your guide. It is also a nice idea to leave behind an envelope with a bit of cash to help pay for anything you have used during your stay, or as a way of treating your host to a dinner out once you're gone. It takes a special person to open their home to you and offer hospitality. No matter what, say "thank you" to the wonderful people who share their home with you while you're away.
The adage about the fish and the smell may be crude...but it is often true. The number one thing to remember is that the general rule of being a houseguest is to stay a maximum of three days. Anything longer than this is likely to start wearing the welcome mat thin, and good houseguests would never want that. Three days of entertaining out-of-town friends or relatives is about all most people can take. End your visit while your hosts are still enjoying your company.