Like when writing a thesis segmenting it with Introduction, Development and Conclusion, film and documentary makers will organize their project in a similar way.
Pre-production is the introduction to your project. By many aspects the most important part of your film, preparing everything in advance. It is like dressing a business plan, not only budgeting your ideas but planning all that the production will need from the revision and correction of the script to the choice of actors or archives to use if necessary. This is the time to think about who you are making this film or documentary for, in short, who is your audience. It is important, you do not want to do what has been already done, some research is necessary. The answer to this question will help you organize better.
This is the time to select the locations and ask local government authorization to shoot, Costumes and make-up if your film is from another period of time, it is the time to select your team, the narrator just in case Morgan Freeman is unavailable.
The decision of the gears to use, the time needed for each sequence and very importantly, a plan B just in case A is no longer possible. Then come the screenplay and shooting schedule
Not mentioning paperwork and agreements to sign. Do not forget your logline, the description in a sentence of what your film is about.
A well-defined pre-production will allow your production to flow nicely.
The pre-production is also the time to think about the kind of music you will need. If you are shooting a feature and want original music, it is indicated to choose the company or composers in advance and share the ideas, the plot, the need for a love theme and other considerations so the composers have most elements allowing the music ideas to flow.
If you are shooting a documentary and feel it is not necessary to have an original score, you may want to give yourself time to choose the adequate tracks from a library. You may even choose a combination, what MUSIC PARTNER calls Music Design. It is the use of existing tracks that could be edited to fit the story line with addition of new tracks if necessary.
Music has become so important in most project, having a partner understanding your needs and being reactive to your demands is essential.