The same soft-skills that are used when reviewing code apply. E.g. asking questions instead of telling or directing, being patient and polite, and giving the other person time to respond. As well as an attitude that even a fresh junior can teach the most senior person new skills. These apply for both the driver and the navigator.
I would be interested to hear other peoples' input on this question. For me, different pairs behave in different ways depending on seniority and whether you two are friends or not.
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