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.
The purpose of a job description is to persuade, as well as to qualify and disqualify candidates before you spend time interviewing them. If you’re looking for someone with a degree in economics, then putting that on the job requirements list will disqualify the candidates without the necessary qualification. On the other hand, the right copy and tone can help you stand out to incredibly desirable candidates.