Or most places. Auto shift rental cars are rare outside North America. Being able to drive a stick should be a basic required life skill, like tying a necktie.

Best advice:

When I'm getting used to a new right-hand-drive car I keep muttering to myself, "Keep left, look right. Keep left, look right," especially if I've flown overnight and feel groggy. Double-specially if I'm careering into roundabouts at high speed.

Days later, though, I'm still mixing up the turn signal and the windshield wipers. Often -- but not always -- the turn signal is the right-side stalk. Much harder to get that bit down than to shift with your left hand.

Finally, no matter how tired you may be or how far you've driven on the left side of the road, you are always working on checking your instincts. If you have to react to some hazard on pure gut -- say a car is coming down the wrong side of the street at you -- you will attempt to do the instinctive thing, which is generally the exact wrong thing. Car comes at you at speed, you will veer right and try for the right-side shoulder despite yourself... when you ought to veer left. Just try to stay out of those situations.

One thing that continues to trip me up is the tendency to walk up to the wrong side of the car. You would think that the more complex aspects of driving an opposite-side car would be the hardest to master, but I can't seem to remember which door leads to the driver's seat!

On the other hand, if I manage to approach the car from the proper side, and I have a passenger walking with me, it's always fun to observe their puzzlement as we both walk up to the same side of the car. They get even more puzzled when I ask, "Are you going to sit in my lap?". Then they see the steering wheel and it all becomes clear.

Just don’t do that during your driving test in the UK, as that is one of the many things that will get you a fail here.

Good advice all around. For most people driving on the opposite side of the road is much worse in their imagination than it turns out to be in reality. As someone who learned to drive in New Zealand, moved to the United States, and drives regularly in NZ, Australia, and the United States I speak from some experience on side-switching.

As others have mentioned the most common issues are the minor frustrations of things in the wrong place (gear levers, windscreen wipers etc). Let's just knock on the head now any fears that the pedals are in a different order!

Obviously the distraction of those frustrations with gears and wipers can be a safety issue. But most of the time there are sufficient cues about where to be on the road that you're unlikely to start driving on the wrong side of the road.

There are three situations which I think are particularly dangerous when you're switching sides, left to right or right to left.
1. Resuming driving on a non-divided open road after being stopped at (for example) a scenic overlook. Without divisions in the road, traffic passing or parked cars, it is very easy to start driving on the wrong side of the road. In New Zealand and Australia you'll see signs at the exits from roadside attractions reminding you to keep left because of this issue.

2. Turning across the oncoming lane into a side street. In a left-side drive country this means turning right across the oncoming lane. When I do this in NZ/Aus after driving in the US, as I am turning I worry that someone is going to come up behind me in the lane to my right and t-bone me as I make the turn. Then I start looking in my rearview mirror for this non-hazard instead of at the oncoming traffic. I've talked to others who tell me they have the same issue.

3. Related to the above, after making a right turn (if driving on the left) into a new street if there are no parked or oncoming cars it's easy to turn into the wrong lane.

You should be fine, but just be more aware than usual. I think that instinct takes over when driving more quickly than it does as a pedestrian. Make sure to look both ways several times when crossing the road. You may find yourself glancing the wrong way as a pedestrian for longer than you are doing the "wrong" thing as a driver.