For some filmmakers there is some confusion as to what a movie is. Movie producers talk about elements that a movie needs, but many film makers aren't clear as to why these are necessary. A movie can be almost anything, really, but if you want people to pay money to see your movie there are some principles that will help out. This isn't an apology for the narrow-minded focus of Hollywood producers, rather an explanation of why they are thus.

Hook

A hook is a simple, easy to communicate encapsulation of the most appealing parts of the movie. A hook can be a simple as "it's Bambi meets Transformers but funnier" or as long as a sentence that explains the action in the film. "An alien comes to Earth and a little boy helps him get home". The reason why they want these hooks is that they don't have much time or attention of the potential consumer to generate their interest. In an environment where there are so many other possible entertainment outlets and a movie isn't based on a franchise this is the easiest way to interest movie goers.

Star

Some people see anything and everything a certain movie star is in. They don't hire actors because they are good at what they do on-screen, they hire them because people like to see them in movies. They are brand names that make people feel more confident paying for a product they aren't completely sure about. They feel at the very least they will get to watch this person the whole time no matter how stupid the movie is.

Genre

If you don't have a star or a hook, you can still garner attention by presenting the movie as belonging to an existing body of work that audiences like. In a way it's the simplest hook ever. For horror the hook would read: "you will get scared", for comedies: "you will laugh". For many people this is enough to get them to see the film. If they have come to develop a taste for thrillers or sci-fi, anything that falls within the conventions of those genres will give these audience members a certain threshold of pleasure.
Genre is the original franchise, in a sense.

Trailer Moments

More and more these days a hook, stars, and genre are not enough. Movies are about pictures and nothing convinces like images. As of late it's become common for movies to be constructed in such a way to be able to fill the trailer with arresting images that will hopefully attract eyeballs. The other elements are still important, but increasingly the money people are demanding five to six moments in a movie they can put in a trailer that make people say "wow".

This isn't the way to make a work of art or tell a good story, rather how to get people to pay money to sit in a seat and watch the movie. There are other ways, and your movie might not benefit from this advice. If you find yourself hearing people mention these things as something you should do with your film, you ought to be cautious because it means someone probably wants to get rich. Indie films often try to include these elements in their films but it doesn't have the same effect. Instead of following what Hollywood does, give thought to the basic thing each of these tactics tries to do. Then do it in a way that complements your film and would appeal to your audience rather than a faceless mass that Hollywood markets to.