Very few people have successfully marketed a feature film or feature documentary, and fewer still have marketed an independent film of any kind. Every successful indie film finds its own path to market.
Every production needs a website. It needs to have a signature image, a poster image, that defines what the film is about. You should test your signature image on your target market to find the one that they like most. A signature image should speak “loud and clear” to your target market. With a sequel, your signature image may be nothing more than a white poster with the title on it, because that’s all your target market needs to read in order to know they want to go. With a first film, your image needs to communicate far more information as a rule.