Fix filmic shortcomings with music
One quite big part of scoring for films that is very rarely mentioned in books is to compensate for shortcomings in the film making. This happens especially at the beginning of a career where you work on amateur or semi pro productions. Quite regularly you will be confronted with bad acting, strange story lines, dialogues that make little sense and other problems that might arise in such a production where the music is required to save the situation a little. Sometimes that will be openly communicated by the director, but sometimes you just need to decide on your own to save a few moments to improve the movie. The most common thing to save some moments from being ridiculous would be to add music even though you normally would not on such moments. This helps particularly well to guide emotions that are not transported properly by the actors or the dialogue. Another decision would be to set a stronger focus on the atmosphere when the production design failed to deliver (e.g. a scene is supposed to feel scary but the lightning and set doesn’t look scary at all, so you add more scariness to the music to compensate for that). Also, connecting confusing editing or story lines with each other by glueing them together with music might be one of these standard tricks. However these things just help to a certain extent. To get back to the example from above: If the scene doesn’t have at least a little bit of scariness, adding a massively scary score to it will just be very ridiculous and alienate the audience even further. So you need to also have an idea of whether the music will have a chance to save something or if all hope is lost.