Poster Criteria

I am beginning to try out different ideas for the film poster, however I was unsure about the criteria that needs to be on the poster as it has to promote/advertise the film. I then found this website which is a step by step guide to what to put on and how to make film posters, he has chosen to mimic an Alfred Hitchcock film.
http://justcreativedesign.com/2008/05/13/how-to-design-a-movie-poster-with-an-example/

Looking at these film posters they tend to be very simple with one object/character as the main focal point and then the title is the other bold thing upon the poster.

In my opinion if a film poster is too cluttered it won't attract the eyes of the audience because there will be too much to understand. If there is one main subject that doesn't give away too much of the plot and a strong title with gives the audience curiosity towards the plot for the film.