Read the script completely before you begin planning. As you read through the script, create a list of all the locations where scenes will be shot.
Research any important background for the movie. For instance, a period piece requires extensive research into the lives of people at the time, place and economic standing of the characters in the movie.
Make a scene by scene list of all the items you need to dress the film sets.
Purchase the props and set dressing pieces you need, staying within budget. If you are working on a low-budget film, try to get as many pieces as you can by borrowing them or by soliciting donations rather than purchasing them.
Stay in communication with the set designer or decorator throughout the process. Communication is vital to ensure that the end result is something everyone is happy with.
Take pictures of the set once it's dressed. After a scene, things may be moved around and repositioned and the reference is needed to put everything back in the correct position for the next take, for the sake of continuity.