A film mix can be a very complicated affair or a very simple one. But there are times when something so simple can get really complicated. The major factor that adds to that is the track layout. For me, I have a very specific basic layout from which the tracks are expanded in terms of their complexity.
Since I use a film mixing console (AMS Neve Gemini), my tracks arrive on specific faders on the board. Unlike some mixers, I prefer to do most of my pre-dubs within Protools. Not that I am against anything on the board or so, its just that I prefer using the board for that analog or non-clinical movement of faders which makes a mix something organic rather than a fixed structure with very defined edges. That would work in trailers because you have only a very limited time and its completely packed, so ducking music just before dialogues etc. will work. That being said, I do make surgical moves, but that is on Protools as it allows me to have those duckings that I would like to consider part of the pre-dub rather than something I want to send unnecessary time on the board. But in the end of the day, the film will dictate to you what kind of a mix it needs. It will talk to you and tell you how it needs to come out. But for all of this, you need a good sound track.
I split my tracks into Dialogue, Music, FX, Foley, Incidentals, Backgrounds, and Songs. These are played back from multiple protools sessions. I like to keep Dialogues and Foley in the same session, Effects and Backgrounds in another and music in the third. This also helps me to have it playback without system load in the plugins that I use.
These are then sent via separate outputs each a 5.1 version, to the console from where I then take it on board for the final Mix.
It is always important for me to have consistency in the session when I set it up. The reason being that when I work, I want to be able to glance to the session and know what I am looking at and what is coming next. I prefer to have my dialogue and music in a Playhead mode so that I can see what is coming. For the effects and background, I try to create a mental map of the session in my head so that it becomes easy for me to make changes while I have an idea running in my head, without leaving the emotional state of the film I am in.
Once I do this, I go ahead to the Final mix.