I didn't do any driving in England; my husband and I agreed that it would be better if one of us did all the driving, so we'd only have one learning curve. Besides, he did it last time too. The two hardest things about driving on the left turn out to be lane position, and right turns. Right turns is a fairly obvious issue, since in the U.S. it's a no-brainer and the left turn is across traffic; fortunately he only turned right into the near lane once, and nobody was coming. Lane position was more subtle; if you aren't used to being in the left lane, you also aren't sure where in the left lane you should be; and you really aren't used to having traffic come at you on the right, so you edge left. We clipped a lot of left-hand curbs the first week or so. The other big issue is pedestrian: which way do you look for oncoming traffic when you cross the street?
Driving in England is complicated by the fact that most of the roads were there centuries before the cars were. They're narrow; they wind; and all too many of them are lined right up to the road verge by 6 foot stone walls, especially in rural areas. (Shoulder? What shoulder?) In some rural areas they're lined right up to the road verge by 6 foot hedgerows which are growing out of 6 foot stone walls; a quick glance to the side just shows leaves, but it's not the whole story. This combined with the American or Continental driver's tendency to hug the left curb makes riding in the (left side) passenger seat pretty nerve-wracking. He says I was very restrained. Of course, in other rural areas there are no walls at all; that's when you get sheep on the road. We saw a sign on Dartmoor warning, "Sheep lying on road," and it was quite right. The other side effect of the walls and hedgerows is that, unless you're driving through something like a national park, you get no view of the countryside from the road. All you see is hedgerow (or wall).
In towns, the streets are not really wide enough for two lanes of traffic plus two sets of parked cars; in fact, they're not really wide enough for two lanes of traffic plus one set of parked cars, and some of them just aren't wide enough, period. We live in a neighborhood somewhat like that, which has given rise to a maneuver we call the "Rockridge do-si-do", where oncoming traffic slows and moves aside into open curb spaces to allow each other to pass. They do this in England, too - but they don't slow. They do it at 35 miles an hour. It still amazes me that the only real accident we had happened at 2 miles per hour (trying to get out from a tight space behind a truck on one of those narrow streets, he misjudged the left distance and forcibly removed the passenger mirror.)
As far as I can tell, there is no custom in England that says you should park facing in the direction of the traffic on the side of the street you're on. People park any old way, sometimes on the sidewalk. If there is a sidewalk.
As cars have gotten wider, so have roads. In some rural areas you find yourself driving past a house (usually a stone house) less than a foot away, because the road has been widened right up to the wall; some of the houses had doors and windows filled in because you can't use them with A road traffic sailing by at 50 MPH, 6 inches away.
We rented a C-class Mercedes because it's a car he knows. In the U.S., this is a smallish sedan. In the U.K., it's one of the biggest cars on the road; but it gets 35 MPG or better. Which is good, because petrol cost 99p (about $2) per liter or about $8 per gallon. If you don't like our gas prices, try $90 a tankful; we have some of the cheapest gas in the world. And don't let Ford Motor Company con you that they can't make small, fuel efficient cars. The roads were crawling with little Fords, they're very popular in the U.K., and since the U.K. is part of the EU, they have to meet European mileage standards. Ford just wants to keep selling F-150s to dumb Americans.