If you are writing for the public, you probably have a very clear purpose in mind, such as to promote a cause or event, to inform or explain a problem, to persuade others to act, or even to entertain.
Public writing should address your target audiences directly. Which people do you most want and need to reach? Where can you find these people? What appeals will get the results you want?
Consider the genre most suited to the purpose and audience of your public writing, and choose the medium (print, online, or both) where the intended audience is most likely to see it. You might create a poster to alert people to an upcoming fund drive, a newsletter to inform members of a group, a brochure to describe the activities of a group, a letter to the editor to argue for an issue, a video to promote an upcoming musical performance, and so on.
It generally uses straightforward, everyday language.
It generally uses design to get and hold the audience’s attention.