Please be careful with your hosts' belongings. In particular try not to break two chairs, two wine glasses, a portacot, a part off a buggy, rip a curtain out of its hooks and ruin a table.
If you spill something, please make an effort to clean it up. Especially if that something is a full cup of soup which hit the kitchen countertop and splashed everywhere, then fell onto the floor spilling soup down the cupboards on the way. Or if it is a cup of coffee on an antique walnut table which my Dad gave me.
Do not fill your hosts' house with cheap ugly plastic tat which they do not want or need, but will have to keep as they know you will look for it next time you are staying.
Do not stay in bed until midday when your hosts have three DCs under 2, get up and have a leisurely shower, cigarette and make yourself breakfast and a drink without asking anyone else if they want a hand/a drink etc.
That was actually quite therapeutic!