Some of the finest movies ever made have been developed by combining genres that may not normally be placed together. For example, Akira Kurosawa made many films combining both samurai and spaghetti western techniques and themes. You may find inspiration by doing just the same type of thing. The 2004 Edgar Wright film "Shaun of the Dead" combined the zombie horror and physical comedy genres to make a zombie horror spoof. When developing ideas for new genre combinations, be specific. Avoid simply combining horror and western. Instead, develop a film that combines psychological horror with traditional western themes.
Another successful approach to developing a great movie idea is to place characters in roles that viewers would not normally expect. For example, you may decide to create a movie in which a priest goes on a violent rampage to restore order to his city. A good example of this type of character reversal is presented in the 1999 Troy Duffy film "Boondock Saints." This film portrays deeply religious men deciding to become mob killers and a detective deciding to join their fight. A typical viewer would not expect religious people to be murderers or a detective to assist them. Writing such a character switch could add excitement to a normal film.
Most superhero films focus on the protagonist fighting scores of villains and a powerful antagonist. However, few films have dared to approach a story from the eyes of the villain. The major reason for this is the difficulty that audiences often have relating to the plights of an evil character. However, such a movie could be a powerful approach to the crowded superhero genre. The film would likely have to feature a villain who was once good and was transformed through circumstances beyond his control in order to inspire pity from viewers. By placing the normally prominent protagonist in the supporting cast role, viewers may be surprised and delighted to see a familiar genre in a completely different way.