I made several mistakes driving in the U.K. three summers ago. The first was picking up the car right away, when I was jet-lagged -- I should have gotten into a hotel for a rest first. Also, in my fatigued condition, I drove from the Glasgow airport immediately north onto the tourist route past Loch Lomond. The highway was two (narrow) lanes, with rocks, trees and dropoffs on both sides, and the tour buses took up a lane and a half. I had numerous close calls, and got into Crianlarich with a traumatized wife, not to mention myself.
I didn't find too much difficulty adapting to driving on the opposite side of the road (since the steering wheel is on the opposite side of the vehicle, it seems natural), but I did have to get used to the position of my left wheels. The solution was for my son to sit in the left front seat (replacing his traumatized mother) and warn me when I got too close to the curb (or, should I say, "kerb"). At that, I made contact several times, and on one occasion bent the rim enough to give me a slow leak, and a near flat tire before I caught it.
The other main problems were remembering which lane to turn into on making a left or right turn, and, of course, "roundabouts". There's only one traffic circle within 300 km of Calgary, and I haven't driven on it in years. Roundabouts are culture shock, but caution and a good navigator did the trick for us most of the time.
An unlooked-for effect was that when I got back to Canada I had to relearn my parking skills. I haven't fully recovered, two years later.
Other than that, no problem!