Location: This is less about the geography and more about the atmosphere. You've been dreaming of a quiet, romantic getaway, but you land at a family-friendly resort overrun with screaming children. This will not make either of you happy—and unhappy people are more prone to bickering. If one of you likes to sit by the pool, but the other needs more action to have a good time, find a place that offers options for both of you in close proximity so that you don't waste time and energy figuring out how you can each do what you want, says Geraldine Rojales, director of guest services at the Kahala Hotel & Resort in Honolulu, Hawaii.
Documents: You know this. You are quite certain that your passport is up-to-date and you always stay on top of your seat assignment. Except...when you forget. Showing up at the ticket counter without the necessary paperwork means someone is guaranteed to lose her temper. Or lose her mind (as happened to someone we know who spent her 40th birthday at the Boston Passport Agency with her husband instead of in sunny Barbados with two other couples). Double-check that both of your passports are up-to-date at least two months out. (The U.S. Passport Agency advises that it takes four to six weeks to renew by mail.) And determine whether you need a visa before you leave; Brazil, India and Russia are three places that require them for U.S. citizens. Although you can purchase a visa upon arrival in some countries, many require you pay in cash (like the Dominican Republic). Be sure to make a stop at the ATM before you get on the plane—or risk trying to find one at the border.
Expenses: Money is one of the biggest issues couples fight about in the privacy of their homes; the stress of traveling, not to mention fluctuating exchange rates, unfamiliar tipping policies and other vacation surprises, can expose fault lines in even the most in-sync couples. Before you go, decide on the total you can afford to spend and figure out where you'll splurge (hotel or private tours) and where you'll cut back (living on cheese and bread for a week). If you're on a tight budget and looking to do more with less, Seper suggests traveling to developing countries like India or Thailand (he and his wife averaged $25 a day on their round-the-world trip) where it's easier to keep costs down.
Weather: Off-season booking will probably save you cash, but it could mean spending your entire trip cooped up with your partner in a hotel room...with only one television channel in English. Check multiple weather sources (not just what your hotel's website says) and find a graph that shows the average rainfall and temperature for the location and month you're planning to travel. Also, research what time of day is the hottest and coolest so that you can plan activities accordingly—and don't end up doing that nature hike when it's 105 degrees outside.