This Rule has some limited application from the JobFairy perspective. In short, you should not reveal anything personal about yourself during the interview process. Employers and recruiters are not entitled to (and in fact, most questions are illegal under Federal law) about your family, children, and personal hobbies. If they respect your boundaries and don't ask you such prying questions, then they are more likely to be OK to work for.
If they do overstep their bounds, you can counter their questions with, "Gee, that's awfully personal", "How is this relevant to the duties of the job for which I am applying/interviewing", or asking the same question of them that they just asked of you. Example: They ask what your husband does for a living. You counter, "What does your spouse do for a living?"
There is no one around to enforce your boundaries but you, so you are going to have to do it. Don't make the mistake of letting them know too much about you, hoping it will make them more interested in you as a candidate. A) Mystery is good, and B) Anything you say can and will be used against you. Don't let slip any personal information, and then it can't be used to disqualify you from the job.