Good question. Actually I'm not sure - I'm just repeating the advice my mother gave me when I asked her. She's a certified proctor for these sorts of things.
At least three different psychologists have told me that the instinctive response is supposed to be the right one. I think it has something to do with how these tests were developed.
Keep in mind that personality tests like these are primarily intended to map out traits of a person's personality in preparation for some kind of psychotherapy. Maybe not so much for Myers-Briggs, I wouldn't know. But the scientific intent of these tests, if you could call it that, is simply to give your therapist an idea of when to start when trying to figure out some deeper issue. (Why you are miserable, unable to work, excessively anxious in specific situations etc.) For that purpose, personality tests are perfectly suitable.
