OK - don't drive on the left-hand side of the road.
But seriously, I drive quite a lot in France so I cannot really comment about other countries. But it is easy to forget that you drive on the right after a stop (for a meal, shopping. overnight etc) if there are no other cues (road markings, other cars etc).
Perhaps the most important thing to consider is that motorists in other countries may be taught to drive in different ways. I find that many French motorists use roundabouts differently from British drivers - they frequently drive around the perimeter of the roundabout instead of moving to the inner lane and then taking a line out at their turning. If you do the latter then you may impeded when you come to your turning. I find tailgating common, too. I think that trying to anticipate other drivers' actions is recommended.
I believe that in many countries there is a general rule of giving way to vehicles entering your road from the right-hand side unless there are specific signs giving you priority. This may be especially the case in towns where "side streets" have priority over apparently more important roads.
Another thing to check is signage - direction signs may not be quite where you expect them to be.
It may be mandatory to carry at least one reflective jacket in the car. It should be in the passenger cabin - not the boot. It may also be necessary to have a warning triangle. In France you are supposed to have a breathalyser - though it is not an offence not to have one.
