Allow plenty of time and don't overschedule. You won't be able to see everything you want to see in one trip, unless you have unlimited time! Save a few things for the next trip
Driving on the Left
Driving on the left is not as hard as you think it will be. Take your time when you first start. Once you are on the road, you won't find it difficult since all of the cars are on the left. On dual lane roads, the slow lane is on the left and passing (overtaking) is on the right. Some roads have a shoulder indicated with a yellow line. If a car is following closely, indicating it would like you to speed up, move to the left into the shoulder and let them pass.
Narrow Roads
On occasion you will have to drive on a narrow local road, only wide enough for one car. Go slowly and pay attention to any spots available for pulling over. If another car comes in the other direction, the one closest to a "layby" at a lane, driveway or other space should back up or pull forward into that spot until the other car passes. The other driver will usually give a friendly wave as they pass by.
In fact, many drivers in rural areas wave as they pass.
Roundabouts are your Friend
Don't be afraid of roundabouts. Take your time and go around again if you miss your exit. The cars in the roundabout have the right away. You shouldn't pull out in front of them. Try to get into the correct lane. If you will be taking the first exit to the left on a roundabout with double entry lanes you should be in the left lane. Get in the right lane if you will be going straight through or using a right exit.
If there is no left exit prior to the "straight through", you could use the left lane. People do get in the wrong lane and horns do get used occasionally, but overall it is not as wild as "circles" or "rotaries" in the US.
I have found that I get used to the roundabouts, look for them when I need to turn back, and get annoyed when I actually get a traffic light!
Speed Limits
Speed limits are now in kilometers rather than miles, as Ireland has gone metric. On highways, the usual speed is 100 kilometers per hour (approximately 60 miles per hour). You will sometimes be on roads posted for 100 kms that do not at all seem like a road that should have that limit. Go at the speed you feel comfortable with until you get used to it and let the other drivers pass, moving to the left shoulder if necessary.
Traffic Calming Points
When you are approaching a town, you will see signs for traffic calming. This is a reduced speed zone to slow traffic down as it enters a town or village. The speed limit will often drop from 100 kms per hour to 50 kms per hour quite quickly when you approach a town.
Gas (Petrol)
Most stations do not have pumps that take credit cards. Otherwise, the pumps work the same was as in the US. Generally, you fill your tank first and then go in to pay. Take note of your pump number and the amount owed. Some stations ask you what you owe, so it is important to pay attention. Many of the larger stations along the highways have rest rooms and shops with food and drinks. You can usually get snacks, sandwiches, coffee, tea, sodas, snacks, anything you want. Quite a few have car washes!