Movie posters tend to be a great example of how genre can be used to market a product. This is mostly because Posters tend to be heavy in content, in the way that they need to deliver a great understanding of the nature of a 2 hour plot into one still composition.
To demonstrate this: Below is the Poster for the film "V For Vendetta".
The poster is composed in a typical foreground, midground background template.
In the mid-ground, features a comic-like composition of the two protagonists (Or arguably in this certain plot, the antagonists) of the media text. This does not only function as a method of introducing the audience to the plot, but also in a way functions as a tool to maintain "Loyal audience": Those who read the comic series, V for Vendetta and are considering consuming the media text for the purpose of loyalty, as opposed to curiosity as to what the plot is based upon.
The background shows a very vague atmospheric Mise En Scene dominated with red whilst maintaining a primary yellow/cyan hue: This produces a colour set very similar to that seen at dawn. This is very relevant to the plot, and will appeal to audience who have a general idea of the anarchistic conceptions carried in the film!
Aside from images: The foreground shows a very common generic convention of a movie poster, which is text.
There are two dominant pieces of text on the poster. The two are very graphically and textually different.
The title, V For Vendetta, is clearly embedded as the top layer of the poster. It is very dominant and does quite contrast in colour and theme with the rest of the poster composition. The red colour has always been known to resemble the type of outrage, anger, agony, anarchism and hatred that is shown in the media text. This fits in to serve the satisfaction of the audience of the teenage to mid-age, mostly male with very biased political opinions demographic.
"Freedom! Forever!" is quite a blunt phrase to be used in this composition, in my opinion. In fact, I'm led to believe that this poster is a fan product as opposed to an official one. Never the less, the phrase explores the subtextual content of the plot via submitting to the audience what the purpose of the protagonist is.
Overall, the poster is used to attract an audience via composing a bunch of generic conventions that would appeal to the target audience. E.g. If you want a teenage target audience, put on show things that will appeal to them i.e. Sex, drugs and rock & roll. et cetera.
As a personal review of the text, I was quite disappointed by the poster as it does not match the standard of Awesome (Aka Audience appeal) that is found in the actual film it's representing!