Just finished 10 days of driving a rental car in Ireland; this is 5th time and here are some thoughts to make it work on left side:
1. You must align yourself from middle of road not the shoulder, once you are comfortable doing this, you are on your way.
2. You must concentrate every second, especially on narrow roads.
3. There are many round-abouts, many! Remember, yield to traffic coming from your right. If you miss your exit, go around again.
3.3. Whenever you stop to eat, get gas or take a break, remind yourself before returning to the road that you will go left not right...might save your life.
4. GPS or SatNav device is good idea.
5. Some Motorways have tolls.
6. Automatic transmissions are more expensive than stick shift. If you rent a stick shift, practice a bit before hitting the roads.
7. When parking be sure to check if a you need to pay and put the receipt in the window.
8. And finally, no matter how fast you think you are driving, you will always average 44 mph!!