First accustom yourself to sitting on the right and become familiar with all the controls before moving the car at all. If you are traveling with a companion, have them remind you to keep left for a day or two, especially at intersections, rounding curves and approaching oncoming traffic. Be especially careful at stop signs and lights. When approaching one slow down and prepare to yield. The traffic in the circle has the right of way and you must yield to it.
Roads range from good to atrocious and since signposts can be confusing getting lost is inevitable.
This is when a good map and advice of locals will help. United States, Canadian and EU citizens DO NOT need an international driver's license. A valid driver's license issued by your country is all that is required in Ireland. Check with the car rental company if you are over 70 or under 21 years of age to see if you can rent from them. Most car rental companies in Ireland will not rent to anyone 75 years old or over.