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.
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.