1) They have a generic title, or use really fugly words. E.g. Duplicity, Whatever Works, The Proposal, Changeling, The Hurt Locker, Funny People
See how uncreative and bland these examples are.
2) Their posters looks yuck. E.g. Whatever Works, Public Enemies, Bangkok DangerousI had to close my eyes when I walked past these foul displays. I'm not going to put them up on this post as I don't want to uglify it. I'll provide links.
POSTERS
Now, I'm going to give examples of how to actually attract the audience instead of repelling them. Here is a run-down of recently released posters that are so well designed, it convinced me that I need to see this movie. A wonderful fusion of art and advertisement.
Funny Games U.S.

Draws you in like a moth to a flame
Persepolis

Simple, yet bold.
The Girlfriend Experience

The art of graphic design, maximised
Anti-Christ

Disturbingly alluring, eye-catching and well executed
Burn After Reading

Great composition. Beautiful typography.
Blindness

Clever arrangement of the title
The Strangers

Creepy. I was obsessed with this movie because of this poster (if only the movie lived up to its marketing).
Doubt

Clean yet striking
TITLES
The title of a movie also has an impact on whether I should see it. When I scan through the list of upcoming releases. There are movie titles that stand out so much that it triggers me to search it on IMDB, here are just a few:
Julie and Julia
Simple, yet strangely elegant. The use of an alliteration is clever too.
How to lose friends and alienate people
Long titles are my favourites. That's why I like Panic at the Disco. But initally, I thought this was a self-help book.
Anti-Christ
Controversy = Appealing
Thank You For Smoking
Thank You For Smoking
They forgot to put the "not"! OMG! Look it up on Google, now.... Oh. It was intentional. Gotcha.
Requiem for a Dream
Requiem is such a beautiful word, even though I have no clue as to what it means.
The Girl Who Leapt Through Time
Not only gave you the title but also a brief plot synopsis, all in one. Nice.