It isn't easy to be a good No. 2 in corporate America. You must bolster your leader's ego while checking yours at the door. You must seek credit without upstaging the boss. At times, you must find ways to object without being objectionable.

Yet business schools and corporations fail miserably in teaching people how to fill the crucial role of top lieutenant.

The first responsibility of a good No. 2 is to win the boss's trust. And that takes time, says Amanda Rose, who filled that role as executive director of Stanford Coaching, a privately held New York company that tutors students for college-entrance exams.

Ms. Rose built that trust by "knowing what I can and can't reveal" to others, by knowing that her boss speaks for the company and by showing a united front to the staff.

That doesn't mean being a yes-person. Ms. Rose recalls a staff meeting where she and her boss clearly had different opinions. Most times, she adds, compromises can be worked out.

And if they can't? Another part of being a good subordinate is remembering who's boss. Mostly, a good subordinate executes. "I don't need someone who's going to give me huge ideas or create the map from the ground up," says Lisa Jacobson, Stanford Coaching's president. "I need someone who's going to make the map detailed and implement it."

She also wants someone who is direct and clear, with an open-minded attitude and a can-do spirit.

If your ambition is to eventually be a No. 1, you must find ways to shine in this supportive role. Find areas of responsibility that the boss doesn't covet or have time for.

Sometimes you shine by handling the minutiae of the business plan or by demonstrating interest and enthusiasm during meetings. Whatever you do, the boss expects you to do it without bothering her.

Being a loyal deputy can get tricky if your boss's interest and that of the company diverge. Going against your boss could damage your career. But if the company is damaged, everyone's career will suffer. It's a tough spot to be in. My advice? Make your case to the boss first. Stress that you feel the situation could damage him as a leader and you want to prevent that. If he still pursues this course, you have a decision to make: How serious a situation is it? It had better be darned critical to the company before you take it to the board or go public. You might even consider finding a new job to distance yourself.