Movies and TV shows are based on themes; Good vs. Evil, Commitment, Decisions, Power of Words, etc. The songs that underly scenes in movies and TV shows, therefore, need to support those themes.
Music layers and folds into the words spoken on-screen and for the most part, is chosen for its semblance to the motive of the scene - not necessarily because it’s a great song.
If you are writing specifically with TV and/or Film in mind, I suggest that you start your song with a 10-second musical motif that introduces the ambiance right away. You should also know which show and which scene you are targeting.
If you are writing with the goal of getting an end title or theme song, then you would target the assignment differently than you would if you were writing for a specific scene. Lets say you want your song to be chosen for the scene where the doctor walks down the dimly lit hallway to tell the wife standing at the end of it, that her husband is dead, then there is a formula to adhere to. And by the way, that scene is happening all the time, over and over... from CSI to Grey's Anatomy...
Eve Nelson is a very highly sought after songwriter for TV & Film because she knows how to capture the emotion of the scene in her music.
Music is an integral part of making a scene come to life.