Find a great script that is not only funny but has a good story. It's not just about jokes. A story that draws a viewer in, making her interested in what happens to the characters, contributes to the likelihood for success of your comedy film.
Find actors who have great comedy skills. These actors should fully inhabit their characters and seem believable in the role. Their delivery should seem natural, and they shouldn't step on each other's lines to get more laughs. Getting a laugh isn't always about flailing your body and talking loudly or in an odd voice, but rather subtleties like a raised eyebrow or a blank expression.
Don't overrehearse. Not only does this take a lot of time and wear out actors, but also the humor can become lost or stale.
Encourage improvisation. While it's good to follow the script, turn on the camera and see what happens. Encourage the actors to include jokes and improvise. These people are comedy actors for a reason: They're funny.
Focus on timing. Comedy is about timing, the right pause, the quick reaction, the sudden occurrence.
Trust your instincts and reactions. If something was funny to you once, trust that it is funny. The long process of working on a movie can make jokes seem less humorous after awhile. Don't cut out a funny joke just because you've heard it 30 times and it's no longer humorous to you.
Cut out weak parts. Even if a weak part has a great joke, it's still bringing your film down. Keep the story pushing forward and keep the pacing strong. Work with a good comedy editor to get your film as tightly constructed as possible. Comedy movies typically move fast, but give time for the audience to laugh. You don't want their laughter to drown out a follow-up joke or comment by another character, so be mindful when editing the pacing of dialogue and humorous actions.