Once you have a target audience in mind, you’ll need to think carefully about where and how you are likely to find them, how you can get their attention so they will read what you write, and what you can say to get them to achieve your purpose.

If you want to convince your neighbors to pool time, effort, and resources to build a local playground, then you have a head start: you know something about what they value and about what appeals would get their attention and convince them to join in this project. If you want to create a flash mob to publicize ineffective security at chemical plants near your city, on the other hand, you will need to reach as many people as possible, most of whom you will not know.