For me it really depends on what I'm being asked to write as the approach for different forms of music comes from different angles.
Yesterday I had several jobs on the go, one was to create a club track that felt similar to a certain famous artist for a 'Pot Noodle' TV ad (yeah, I get all the good gigs
) - for that job it was all about the big banging drum beat so i started from that with no idea what I was going to do musically on top. Once that was up I wrote a melody for the singer, recorded her and a small stack of backing harmonies - once she'd gone I then decided how to harmonise what I had - ended up with three versions one in the dark minor key, one with a suspended feel and one happy tonic major key. So that job was very arse about face.
The other job was scoring a kids cartoon - lots of music all written to work with the action on screen so every movement of every character, reaction, mood and change has to be pointed up in the music and must also feel like it belongs to the sections either side of it so the music must all join together as well - For this type of work I deal with small fragments at one time working vertically not horizontally across the time line - you may have a section where a character wakes up in his bed......the door to the room slams open and another character runs in.. So you have to establish each element of that so the music points out these things ... that may be six beats of calm sleepy strings with celeste and harp...then smash ! drums, basslines and guitar for 5beats, reaction sting, pause and into a short picked guitar pattern for three bars... Totally fragmented writing with a huge range of instrumnets, colours, tempos, grooves and effects. Little tiny bits of music all different but all linking to sound right and look right.
The final job of the day was a short TV ad for Moneygram - this had to be a bit 'Harry Potter' - mystical and magical with a key moment when a girl in the film levitates - started with riffing on the piano, decided on a basic chord pattern - but before recording set up the click track to find a tempo that would give a good a nice even number of bars at the top but land on a good downbeat when the girl's feet left the ground - this was difficult as the beats never really worked out... then decided to try a 3/4 time sig... bingo that worked. Mapped out the piano sequence simple cliche (Cmajor to Dmajor over C repeated ) - at the bar the girl levitates I added boys choir, harps, celeste, strings and windchimes but with a big key change up a minor third - tailed off with big resolution held chord......done and dusted in two hours.
All very different tracks for different types of client and all totally different in approach to production and composition.