Propaganda is used to attract other individuals to a particular cause. However, the techniques involved in propaganda usually seek to play off of some sort of weakness, insecurity or desire of the audience to whom it is targeted. Therefore, there are specific strategies that a person using this device would employ in posters.
Everyone Is Doing It
Show statistics on posters that show that a vast number of people are involved with a particular cause. For example, you might want to say that only a certain percentage of people in the town vote Republican in order to try to sway the people to vote Democratic and support their local efforts. You could also show a picture of a number of people supporting a particular cause, such as pro-choice legislation or a walk to ensure universal health care.
Tactics Against the Opposition
Instead of highlighting the positive aspects of the position that the propaganda seeks to support, sometimes the poster will want to show the negatives of the other side. For example, you could list the reasons why your side is right and the reasons why the other side is wrong next to one another. Furthermore, show what the enemy or opposing side has done in the past that has had detrimental effects on the community or organization.
Assertion
Make clear-cut statements that support your option as the best. Generally, a propaganda poster is not going to include evidence, because the poster does not want to open too many doors to the audience, for fear of them finding out something negative about the product. You might use quotations from someone from a newspaper or a popular celebrity on television to give the statement that you are trying to make some more credence to your audience.
Relating to the Audience
Provide information about who is sponsoring the poster on the actual poster itself to make that organization or group seem more relatable to the target audience. For example, if you are trying to convince poor workers to rise up and protest against the constraints placed against them, place a brief story and picture that shows a member from the organization who says that he went through a rags-to-riches story in his own life.