A great thing to keep in mind whether you are using a song or score with your film scene is to be mindful of closing cadences. A cadence is a musical term to describe an ending point. In classical era music you often hear a series of chords that set up the final resounding last chord. Pop songs also usually have clearly defined endings or fadeouts which signify the end.
If you want to keep propelling the dramatic action forward, edit your music so that it never ends on a finality. It stops the dramatic action and subconsciously closes the curtain. This may be useful for the end of Act 1 in your screenplay, and yet it also may stop the action too early.
Martin Scorsese is currently working on a film called “The Departed”, (a remake of a 2002 Hong Kong film entitled Infernal Affairs) and Howard Shore is scoring. According to Tim Starnes (one of Shore’s right hand men) Scorsese is very much attuned to the “curtain calls” in the music. Whether it’s song or score, he often edits the piece to start after the beginning and end in the middle.
If you are working with a Composer, you can bring this up in conversation early in the process.
One way Composers can avoid the “dramatic finality” is to avoid the use of the tonic (the root note) in the bass. As orchestrator Deniz Hughes likes to say, “putting the tonic in the bass is the dramatic equivalent of sitting in a chair. You’re not going anywhere. You’re static.”