To make any trip run smoothly, there are a few things you should take care of before you hit the road. To start, you should find out as much as you can about the destination you plan to visit. Learn about what to expect in terms of culture, weather and local customs. Try to pick up a few common phrases of the local language if you can: yes, no, and thank you, will often do the trick.
Make sure you have the proper documentation for your trip including passports, visas and tourist cards. If only one parent is travelling with a child, you may also need a notarized letter from the other parent giving consent for the child to travel.
Bring some cash along but don't bring too much, alternatives include credit cards and ATM cards and travelers checks. Most countries have ATM's available and often getting cash as you need it is the way to go. Try to avoid currency exchange at the hotel, they tend to have the highest exchange rates.
Will you need to be immunized? Find out what the requirements are for travel health at your destination. Never travel without travel insurance, a broken leg in a foreign country can set you back $20,000 out of pocket. It's not worth the risk of not getting proper medical attention when you are far and away.
Where can you get all this information to plan your trip? The internet is of course a great place for information, other sources are friends and family who have traveled to the destination, travel agents, a library or bookstore, Embassies, Consulates and tourist boards. If you are going on an extended trip, a guide book on the destination is a great resource to bring with you.