Be prepared, open and willing to compromise, and compromise hard. Especially if your budget isn't anything flash.
Also, ego goes out the door when you're making a film. It's one big collaboration and if everyone is pulling in different directions, it's going to be a bad time. Be open to ideas and willing to embrace them. Prosecute your ideas and be ready and willing to have the creative discussions you need to have.
Work with people who get you and avoid those who undermine you. Work with people who challenge you creatively, not just those who are complicit.
Respect the hierarchy, but develop good pre-production protocols that allow you to really challenge the creative decisions and direction before you get to set. When you're on set, you're all making the same film. Be easy to work with and get along with - you'll get hired on the next one. Make sure you're creating a very safe environment for the actors to work in and to feel comfortable being vulnerable in.