I will tell you my experiences. Two years ago I rented a car from an urban location in Hokkaido. I'm in the car with the rental car lady who's showing me how to use the GPS and tells me which gas station to go to. Then she says "see ya" and suddenly I'm left to my own devices to drive this car out of the parking lot which directly leads out to a busy intersection. It's like being thrown into fire. I'm sitting on the 'wrong' side, everything's backwards, and it took some courage to get going. I needed to think ahead of time how I'm supposed to turn left at this initial traffic light. Once you negotiate that and start driving amongst other cars, you quickly build up confidence. However, the thing that will continue to get you is the wiper blade vs turn signal thing. You will get that mixed up all the time. When you have to turn at an intersection, just follow the car in front of you. When there's no car in front of you and you're the first or the only one turning, you have to think hard and remind yourself in advance how you're going to turn and where you're going. But after a few hours, all of that gets more comfortable. However, just when I thought it was becoming piece of cake, I ended up driving on the wrong side one day and looking really stupid (not to mention dangerous). So you constantly have to keep reminding yourself "left side! left side!"

Last summer I rented from a place that was in more of a quiet location where getting out of the agency parking lot was a lot less intimidating. That certainly helped me ease into things.

I really don't think taking one or two lessons on driving on opposite side is going to help. Driving is driving. The only thing inherently different about the car is that wiper blade and turn signals are flip-flopped. Pedals are the same. The thing that's key is constantly reminding yourself to drive on the left side.