First script reading
read through the scrip, let the scenario play out in your head, document any and all sound you hear (dialogue, environment, general ruckus) the more thorough the better. Also listen for non diegetic sounds, what sound effects do you hear when the scene plays out in the context of a player?
group your sounds into categories, balance them out in order or importance (IE voice louder than general background chatter)
Separate the sounds into: concrete, musical, and voice sounds.
Concrete sounds are sounds that fit with the diegetic, for example a clock ticking when a person looks at a watch.
musical is when that sound is played out of context for dramatic effect, for instance theres no clock yet we hear ticking begin to slow down in a time freeze sequence.
voice is pretty self explanatory, just the voice of the characters.