Film teaser posters

Before creating my own teaser poster, i have research some famous and successful ones to see what conventions they follow. although similar to actual film posters, they are usually published a while before the film is released, as a way of drawing in the audience with its sense of mystery. Here are a few i found to be most effective.
I have noticed that each poster contains one stark central image to drawn in the eye, and little text. The Dark Knight poster and the Happy Potter poster both include a tag line and film title, whereas the X-men poster only includes a release date. this simplicity is effective in creating suspense and excitement towards the release date. we can tell that each of the posters belong to established films with a large fan base, due to their ambiguity, not needing to give to much away but as the same time the audience knows exactly what film is being advertised.
Another aspect that all three posters share is effective lighting. the Harry Potter and X-men poster both include well lit faces in good quality, in faded black backgrounds to draw more attention to this central image as well as further adding to the mystery. Similarly, The Dark Knight poster is dark round the edges, and the main lighting is thrown upon the central image which is effective in catching the eye.