If you are DC, you don't. You leave that to the guys across the way. It's also why Marvel won't be advertising for the new Atom TV show, being that the character is part of the line-up of the Distinguished Competition.
Marvel is currently marketing Avengers: Age of Ultron. A trailer for Ant-Man will be attached to the Avengers movie. I suspect there will be a reference to Ant-Man in the Avengers movie somewhere.
I just realized who is playing Ant Man I love that guy, but as an action movie hero? Idk anything about Ant Man comic wise but, if his personality fits with Paul Rudd acting style, it could be a great movie... or another Green Lantern