Ceiling Joists... help!?

I am having a hard time finding a joist in my ceiling. I need to drill a hole where there is a joist. Stud finder is not working. My ceiling is regular drywall... so i dont know how to find it!! I do have a ceiling fan which im uming is on a joist, however, i dont know which way they run!!! Do they run towards the door? Or parallel to the door frame?? Please help! Im in the US.. if that helps...