I had heard some horror stories before going, and I was really worried about driving in Ireland. However, once we made it through the first roundabout, nearly killing ourselves, it was pretty easy.
It's better to have a driver and a navigator, so the navigator can look for the miniscule - and often absent - road signs, while yelling "Stay left, look right!" to the driver, in case she forgets.
We agreed that the most thrilling part of driving in Ireland was on the part of the passenger. You always think (being on the left side of the car while driving on the left side of the road) that you're going to hit something on the side of the rather narrow Irish roads. And the roads are very narrow, especially so in the countryside, less so in the big cities like Galway and Dublin. One road we ended up on could only fit one car, and had stone walls on both sides! The roads are also quite winding.
Also beware, that people in Ireland don't have parking garages, and we only saw one parking lot the entire time. They just stop on the road, either side, with their car pointed either way - doesn't matter. This makes your lane even more narrow.
For roundabouts, try to decide before you get there whether your road is the first, second or third exit, and get in the appropriate lane. For example, if your exit is first, stay in the left lane. If you're exit is second or third, get in the right lane (or middle and right lanes if a bigger road.) Make sure to yield to traffic in the circle, which means LOOK TO YOUR RIGHT. Once it's clear, enter carefully, watching that everyone isn't really in the appropriate lanes and going every which way, and exit when appropriate. We were told to stay in the circle if we missed our turn. I'm not sure that's possible, but we tried our darndest.
For road signs, don't expect much. We relied a lot on our intuition - getting lost only when we second guessed ourselves. Don't be afraid to ask for directions, many times, because Irish folks, while well-meaning, aren't the best at giving directions. We found that taxi drivers were the best folks to ask.
The maximum speed limit on the main roads is 60 miles per hour, 30-40 miles per hour on the smaller roads, and there are encouraging signs everywhere that tell you how many people have died on the roads in that county this year and to think about your driving. I'd go much slower on the twisty turns, least a big truck be coming the other way. That was the scariest part for me!
The best thing I did to prepare for my driving trip was visit this web site: AA Route Planner. The site lets you enter your destinations and gives pretty good directions (better than you'll get from an Irishman!) Even if the road doesn't have a name, it'll give you estimated time on that road, the towns you'll pass through, etc.
Note to rental car drivers -- GET THE FULL INSURANCE! With the narrow roads, the bad drivers, the twisty turns, the stone walls on both sides, and being an American driver, the $20 a day for the insurance will save you over the scratches and nicks you'll inevitably put on the car.