Be time considerate. Though my own internal clock seems to be set about a half an hour behind the rest of the world, I recalculate it so that I can arrive on time for a party and, if I plan on arriving later or I get unexpectedly delayed, I call.
Never arrive empty handed. Cupcakes to a barbeque, wine to a dinner party, squirt guns from the 99c store for kid's birthday parties and afternoons by the pool. Bring something.
Always clean up after yourself.: Wipe down the sink when you use the bathroom, wash the glasses you drank from, straighten up the room you were sleeping in, put your empty beer bottle in the trash. Your host is not a maid service.
Don't overstay your welcome. Your hosts are happy to have you; they're also happy to see you go.
Write a thank you note. Though a snail mailed card with a bunch of flowers is the old skool way to go, a card alone, even a simple email or text is thoughtful.
House Sitting or House Swapping
Bring your own food and take it out when you go. No one wants to deal with your half-eaten leftovers.
Leave the house cleaner than you found it. Even if you don't do it at home, wash and put away all the dishes and all the sheets and towels you used, remake the bed, wipe down all the counters and the sinks, Swiffer the floor and clean the toilets.
Stock the fridge. If the homeowners will be coming home within the next day or two, buy a few staple groceries. A dozen eggs, a carton of milk, and a loaf of bread means they won't have to immediately run out to the grocery store.
Leave something easy for them to eat. The owners of the home I recently house sat for were coming home from Europe after a chaotic day of planes, trains and automobiles in order to make their connection for their flight home. They'd likely be too tired to even see straight, let alone cook or even order out. I left them a simple meal, easily prepared. Even some good cheese and a bottle of wine is nice to come home to and makes the job of transitioning back to the real world a lot easier. Flowers are also nice (though if they're not coming home for a few days, definitely skip anything that might rot or wilt).
Give a house gift. If you don't feel comfortable leaving food, a nice bottle of wine or a simple gift of something you've noticed they need (a good wine opener, a new bath mat, kitchen towels or small kitchen gadgets are the things I've found most peope could use), is always appropriate.
Leave on the air or heat. It's always nice to come home to a house that's perfectly temperate.
At the Pool
Bring your own towels. Though people with pools often have loads of extra towels, don't assume this is always the case. Bring your own.
Don't hog the bathroom. You're just changing into something dry, not preparing for a ball. Get in and get out quickly and save the primping for when you get home.
Bring an arrival gift and a departure gift. Come with something great to eat or drink and leave or send something for the house when you leave. A plant or flowers are always nice.
Plan to spend some time alone. Bring a book, plan an outing, take a drive or a walk and give your hosts some alone time during the weekend. They're hosts, not tour guides, and they'll probably need a little downtime from entertaining.
Offer to help cook or buy groceries. Planning and preparing meals for more than the usual number of people can be exhausting. If you can't cook, then take charge of going out to buy groceries or offer to take everyone out for breakfast or order out lunch to give your hosts a break.
Help with the clean up at the end of the weekend. Even if all you do is strip the bed and gather up the dirty towels, it helps.
(Image: Chris Perez for Cheyenne Weaver's Gilded Simplicity)