If you've been travelling you'll know exactly what I mean, if you haven't but are looking to go, I would read and adhere to these rules in order not to piss off your fellow travel companions.
1.) This isn't so much a rule, but a personal thing for me. Please do not wear these types of fucking sandals.
I don't care how practical or comfortable they are, they're FUGLY! Even worse if you wear them with socks. If you're not down with flip flops, there's plenty of alternatives such as Birkenstocks which are making a huge come back.
2.) Thou shalt not be a snob - no matter how comfortable and nice your life is at home haven't you come to escape that? To get as much as you can from travelling you have to experience it - so eat that street food, stay in hostels, take time to talk to locals. You'll learn so much more, and my motto if anything goes wrong is "Well it makes a good story".
3.) Thou shall learn to compromise - If you come in and everyone's asleep don't be the annoying person to turn on the big lights, things like that. Actually forget travelling, being able to compromise is a life skill and one you'll get a lot further with, plus people will like you a lot more for it. Obviously don't be a push over but don't throw a tantrum like a baby if you don't get your own way. Not cool bro.
4.) Thou shall come away with an open mind - Narrow minded people are some of the most unattractive. When travelling the likelihood is you've come to countries a lot poorer than your own. Cultures, people and everything in general will be different. Learn & respect it. There is nothing worse than seeing people behave like those 'Brits abroad' programmes you see.
5.) Thou shall take responsibility - if you're travelling in a group or with another person, share tasks. It's so frustrating when it's down to one person to book flights, accommodation, buy tickets, find out what time the next ferry is etc.
6.) Thou shall not piss the bed - thankfully I've not experienced this but have heard of people it has happened to. This is why I ALWAYS take the Top Bunk when staying in dorm rooms. No matter how drunk you are, the toilets are never that far away. I'm talking to you in particular boys!
7.) Thou shall book a private room if I have an 'over night guest' - You know what I mean. This one I have experienced, in a bunk bed below me. I'm not easily offended, but it does make it rather awkward for everyone around. (More often than not, these sinners will make a quick get away and avoid eye contact in the mornings).
Most importantly; HAVE FUN!