Here’s a sample of job descriptions, ranked from good to bad. Looking through them alongside their scores makes it obvious why some are better than others, and is a good exercise to teach yourself to get better at writing them.
Typically, organizations use their human resources or personnel department to create job description templates. In some cases however, a departmental group, a manager, or another individual (usually the direct supervisor of a position) might be responsible for creating one. In any case, make sure the creator of the template is familiar with the company’s or organization’s needs.