As soon as you know that you will be traveling out of the country, make sure that your passport is in order and that everything about it is valid. If the emergency section of the passport isn't filled in, make sure that gets done. Is your photo up to date?
Another thing to check on as much in advance as possible before your trip is whether or not the country to which you will be traveling requires a visa. If so, and you don't have one, you need to begin that process at the earliest possible time. Another fact you will need to know is if there are any restrictions on a visa issued to the country that will be your destination.
You will need to find out if any particular immunizations will be needed before entering your destination country. Even if a vaccine isn't mandatory, are there any health risks that you would want to be aware of? Be sure to have your insurance ID card with you on the trip (on your person, preferably, and not packed in a suitcase) and know if the hospitals close to where you will be staying would even accept your insurance or if treatment outside of America is covered by your insurance company. With your ID card, have a list of any drug allergies you may have, any pre-existing medical conditions, and a list of any medications you are taking.
When In Rome ...
The old adage of "when in Rome, do as the Romans do" is very important when traveling to certain areas of the world. If your destination is a region that does not enjoy the same basic freedoms or beliefs that America does, take the time to research those things. Know the customs and the rituals and know which kinds of actions or behaviors could possibly cause trouble for a foreigner in that country. Waiting until you arrive and hoping you will catch on to the customs after arrival is much too risky.
Also find out where certain things are located near where you will be lodging. Where is a grocery store and pharmacy? A police station? How far is the nearest American embassy? How far is the nearest hospital?