It must be one of the most thrilling moments of an executive's career—the call to lead a company. With the new office come new responsibilities, new excitement, a sense of accomplishment, and, unfortunately, a high risk of failure: within three years of the appointment, one-third of all CEOs chosen to guide US companies are gone.

Experience shows that getting a good start is essential. Much has been written, of course, about a CEO's first 100 days. But what about the weeks and months before the job even begins? What can newly designated CEOs do to improve their chances of long-term success in the vital period between taking the job and taking the reins?

To help answer these questions, we interviewed 15 current and former CEOs of US companies about their choices and lost opportunities during the period just before they took over. The annual sales of their companies—in a cross-section of sectors from high tech to financial services to consumer goods—range from $1 billion to more than $25 billion. Most but not all of the CEOs were considered successful in their roles. Our group was about evenly split between external and internal hires, and none were founders or members of...