Intersections and roundabouts are where the instinct fails first
On a straight road, left-hand driving corrects itself fast — you’re following the car ahead and the lane markings do most of the thinking for you. Junctions are different: your first instinct after a turn, especially a quiet one with no other traffic to follow, is to settle into the lane you’d use back home. Slow down more than feels necessary at every junction and roundabout for the first day, and consciously check which lane you’ve landed in before you accelerate.
Expect to signal with the wipers, at least once
On a right-hand-drive car, the indicator stalk and wiper stalk are swapped from what you’re used to. Reaching for the indicator and getting a windshield wipe instead is close to universal for new-to-Thailand drivers, and it’s harmless — but it happens most in exactly the moments you need the indicator working without thinking, like a roundabout exit. A quick stalk check before you drive off from pickup saves the surprise later.
Your blind spot has moved
The mirror you’d glance at without thinking is now on the other side of the car, and your natural blind-spot check — the shoulder glance before a lane change — needs to happen over the opposite shoulder. It doesn’t take long to relearn, but it’s not automatic on day one, so give lane changes an extra beat until it is.
The first 30 minutes matter more than the rest of the trip
Most of the adjustment happens in your first half hour behind the wheel, not over the whole holiday — and that’s exactly when you’re also dealing with a new car, a new route, and possibly jet lag. If you can, start on the quietest road available — a hotel driveway, a resort access road, a soi with little traffic — before merging onto anything busier. Ten minutes of low-stakes practice does more than any amount of reading this page.