Plan everything in advance -- including downtime
Yeah, this is important. If you're going to a country where neither of you speak the native language, you're going to want to make sure you don't end up in a confused tizzy the entire time.
First of all, learn some of the language basics, so you can get around. Key phrases like "where is the nearest hostel?" or "please show me the way to that kinky couples brothel" will keep you from getting lost and ending up in that other hostel where they eat people.
Along with deciding if you want to make your vacation about sightseeing or getting lost within the culture of the country, you should always plan some downtime. This is especially true if you're visiting a country with a huge time difference. You may think you can stay up all night when you're jet lagged, but your body is going to tell a far different tale.
There's nothing wrong with lying down and recharging on vacation.
Get outside your comfort zone
Maybe it's my chronic apathy and distaste for youths talking, but visiting a historic landmark has become infinitely less exciting with the inventions of Google, Snapchat, and Instagram. At this point, everyone knows what Times Square looks like and shouldn't waste their time navigating the cluttered streets and expensive restaurants when they can just watch their friends do it on their phones.