Driving in Ireland is like re-living high school driver's education. Those hazards that seem to only live in the safety movies will show up every day in Ireland (e.g., Irish sheep lose their charm when in middle of your road after coming 'round a blind bend).
Roads are narrow with little to no run-off; stone walls are frequent. An oncoming tour bus can seem massive and unsettling. Add factors like variable weather, tractors, livestock, slick and/or poorly maintained road surface, unfamiliar directions, piloting an unfamiliar European rental car, inexperience with left side driving, and fatigue if you've just arrived... and it all adds up to take it easy!
Budget your driving time and distance at 35 miles per hour (56 kph); add getting a little lost as well as a stop to stretch the legs and snap pics. Help the driver with maps and directions. If traveling other than summertime (when days are long), check a newspaper when sunset is and plan on arriving an hour beforehand. Your passengers and your own nerves will thank you. Plan your itinerary with a day or two without the car. And try to plan Dublin or another big city at beginning or end of trip so you can get free of the car ASAP.
On arrival, if pubbing is among your things to do, consider proximity to accommodation. Stay in town or within walking or taxi distance. After some finger wagging by the EU to improve road safety, Ireland has, this decade, really cracked down on alcohol and driving. Don't do it. Enquire at your accommodation about taxis and take the cabbie's biz card so you can summon a lift home.
When renting, be sure to confirm drop-off locations of your rental company. For example, not all rental firms can accomodate drop-off at all airports. This can affect either your itinerary or your choice of rental firm. Select a car that suits your needs and try to enforce among your travel mates, prior to departure, some sort of suitcase size discipline. A good rule of thumb is that a so-called four passenger car is really, with addition of luggage, a three passenger car. If your party is a foursome, consider two smaller cars. The not-so-preferable alternative could be one vehicle large enough to hold four people and all that luggage... on narrow Irish roads (and now this has come full circle). Safe travels!
