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.
Write a description of your company or organization. This overview will be included with all job descriptions, to give a sense of your workplace. Thus, it can be written ahead of time so that it can be inserted into the template when you prepare it.