The best way to create and manage consistent, concise and effective job descriptions is to start with best-practice job description templates. A well designed template ensures employees, managers, HR and the organization overall get all the information they need, while making the associated tasks easier for everyone.
Prepare job summaries, if relevant. You can use the job description template you use for each position that you advertise by filling in the template with the information that is relevant to that position. However, if you do (or expect to do) a lot of hiring of a particular position, you might make a special template that includes a summary of that job. This will save you some time.