Make it relevant. Make your tagline relate to your movie. For example, the dance movie "Step Up" would have left people scratching their heads if its tagline was "Let's cook something together" instead of its actual, "Two worlds. Two dancers. One dream."
Be creative. Describe the movie in an interesting way that catches people's attention. For example, "Stranger Than Fiction" uses "He's not crazy. He's just written than way," which is much more creative than "Someone is writing someone's story."
Be concise. Ensure that your tagline provide information about the film but does not summarize the entire film or require much reading from the audience. For example, "Stage Beauty" uses "She was the first of her kind. He was the last of his," which sums up the gist of the movie without being too long or giving away too much information.
Make it memorable. Write a tagline people will think about for days after they hear it. Script it so that people will be able to name the movie from just the tagline. For example, the "In space no one can hear you scream" tagline from "Aliens" was voted the top tagline almost 30 years after its release.
Pique interest. Ensure that your tagline leaves people wanting to know more about your movie. For example, the tagline, "Some war stories will never make the nightly news" of "Gunner Palace" is much more intriguing than, "A story inside a palace."
Make it original. Unless you are doing a spoof of a well-known movie, keep your tagline fresh and new. For example, the tagline, "No one will hear you yell if you are in outer space," is not original.
Play on words. Taglines that play on well-known phrases or make people think twice are likely to garner attention and be memorable. For example the writers of the "Chicken Run" tagline came up with "Escape or die frying," an adaptation of "Escape or die trying."