While no longitudinal study has yet examined the entire working life of any group of Americans, which would be necessary to compile data that statistically documents how many job changes may be expected during one's work life, many career counselors advise that Americans between 18 and 35 typically change jobs as often as every 18 months, while those over the age of 35 are likely to change jobs, or even career fields, every three years. Each of these job changes requires similar preparation, no matter how similar or different the jobs may be.

The first step in securing a job—whether it is a part-time first job for a 14-year-old, or a midcareer change of fields for a successful business executive—is to research the job market. What jobs are available? What are the educational or experiential requirements needed for employment? Will a move to another part of...