Met with my songwriter today!!! It went amazing. Can't wait to hear what she comes up with.
Here are some tips from my brother Dan (a composer and DJ) on collaborating with musicians for film:
1.) Even though it is the musicians job to write what you ask for, you can't expect the musician to create anything outside the limits of their abilities. If you're working with a jazz musician, then she'll probably only be best at writing jazz.
2.) The musician may also be limited with instruments. If you want real instruments, like piano or guitar, then it can get expensive and difficult to record them all. If you're okay with synthesized instruments, then it will be easier to add a fuller (yet faker) ensemble of instruments.
3.) When talking to the musician, be careful when using words like "beat", "rhythm" "melody" etc. A lot of musical terms can have different meanings depending on the context, and it could make the musician confused. Try using non-musical words to describe what you want, like "cheerful" "nervous" "fast-paced" "panicked" etc.
4.) Always keep in touch to see how things are going. Musicians are flaky sometimes, so they might forget about the deadline if you don't stay in touch often through email or phone.
5) Most importantly, a film-musician is just like an actor. They take a lot of pride in their work, and can get sensitive when it comes to criticism and comprimise. So if you lay out your expectations as clearly as possibly from the very beginning, and don't change your expectations throughout the project it will go smoother. If you don't give the musician a clear precise outline of the music you want from the beginning, the musician will not be pleased when you say that you want them to do something different than what they started.