Give it bite. If it's an action movie put an action scene right up front. Make your film start like most films end - like the intro sequences to James Bond movies or the start of Indiana Jones. Classically this would probably be called a prologue - a prelude to the rest of the film. Body - This is the main chunk of the film.
Stuff happens, usually to one person who's fighting against it.
Pretty much like an Act Two. Plot elements and characters come to the boil. Ultimately we see where things have been heading and as a result of their actions characters change and grow. Hitchcock said that's all his films were - a great scene which the rest of the film hangs around. Funny how it's elements like Psycho's shower scene and the attack on the school in The Birds that are remembered best.