The hardest habit for me to break was crossing my hands on the steering wheel -- like doing a maneuver or something that required turning the wheel a lot with both hands.
I don't know what the examiners are like on these little points nowadays, but when I took my British test back in 1983 they were quite picky on this sort of trivial thing. Feeding the wheel through your hands a few inches at a time the way they want always seemed like making a simple task needlessly complicated to me.
Another point I could never understand their obsession with was insisting on the parking brake (UK = "hand brake") being applied every time you stop at a light or a stop sign for more than a couple of seconds.
Still, at least there wasn't the complication of the theory and perception tests back then -- Just the practical drive followed by a half dozen Highway Code questions posed verbally by the examiner while sitting in the car. I could never understand why they didn't do that part
before the drive though.