The fact that you are sitting on the right side of the car makes it perfectly natural to drive on the left! I agree completely with Irishfan---focus on the white line, the approaching driver and forget glances at the ever present wall. BTW, I'm a senior and I learned to drive with a manual transmission. If you drive a manual in the states, or are confident driving a manual, by all means rent one in Ireland. It's MUCH less expensive, and as sitting on the right and driving on the left feels normal, sitting on the right and shifting with your left hand also feels normal. Thank goodness the pedal arrangement remains the same. lol
Admittedly, last year when I first visited Ireland, I was concerned about driving on the left as I had not done it since the mid 70s in the UK. However, it all came back very quickly and this year I was feeling very confident about it. (Until I picked up my Dooley rental car with 7km on the odometer. No dents, no scratches--it was perfect!! Nothing I could blame on a prior driver. Happy to say I returned the car with over 3500km with no damage what-so-ever.)
A comment about the roads--the M and N roads, especially the Ms, are boring!!! I guess they are ok for getting from A to B but forget seeing anything!! Avoid them if at all possible. Take your time, drive the smaller roads and see what Ireland is all about!!