There's a lot of things to consider before driving internationally. The last thing you need is for your vacation to start with either a car accident or getting pulled over for not having the proper identification. Here's a few things that I make note of before embarking on my journey.
IDP - The first and most common form of identification that people look into is the IDP - International Driving Permit. The common misconception is that people usually think this allows them to drive in other countries where all it actually does is translate your current license into multiple languages. This is very beneficial if you're traveling to countries that speak in different languages but would hold no value if you were to travel to English speaking countries like Australia. My recommendation is to look into the territory that you're traveling to to confirm whether or not you can drive with your current license.
Language Barrier - Speaking of translating your license, another thing to consider is the language barrier when reading directions and signs. For example, I was unable to read the signs in China since they were not in English (nor did I expect them to be, though that didn't make it any easier).
Foreign animals - Need to be careful of the wildlife when driving in different parts of the world. Those of us from NYC are great at dodging jaywalkers but not used to wildlife jumping in front of us. We do know if we're upstate NY a deer can pop out at any time, but what we're not used to is the wildlife in places such as Australia that can jump in front of your car in night in the middle of the outback. Recommendation from locals is to drive during the day until you're aware of your surroundings.
Traffic Patterns - Need to determine what side of the road the country drives on before jumping in the vehicle. You've been driving on a specific side your entire life, switching over can slip your mind when making a turn which could be a disaster. Other things to be weary of is how the specific country or state makes turns. For example, most places in NJ require a jug handle in order to make a left turn from a multi-lane road where as other states don't have them.
Local Laws - Every country and state is different, it's important to know the local laws before driving in a new place. If renting a car, be sure to ask for differences or odd laws before leaving.
Documents and Info - Be sure to have the proper identification with you, especially since a Drivers License may not be sufficient if you do run into any difficulties. Also need to make sure you have all the proper information in case of an emergency. What if you have a flat tire? What if you need an ambulance or get into an accident? This contact information is different in every country, definitely want to know who to call beforehand to prevent a situation from getting out of control.