Posters, in general, are an effective means of communicating complex information in a simplified and approachable format.
Effective posters will have not much time to convey its message. Therefore the message being delivered has to be done clearly, easily and without much preamble or other context given.
An essential element to creating an effective poster is paying mind to the aesthetics of it – it must be visually pleasing. You have to visually pull in your audience member to talk to them.