For me it really depends on the project. My music always revolves around electronic music, but I write for so many different disciplines (music for my own amusement, for film, tv ads, dance choreographies, etc) that it is impossible to always start with the same approach.
For club oriented songs, I will most often start by building the groove - as that is what will make or break the song on the dancefloor.
For films or tv ads, what is happening on film and the director's vision will determine the approach, the mood, etc.
For dance, I have been experimenting with various approaches in working with choreographers. One of them is like this. We will map out a theme, say "water". Then we will pick a tempo or various tempo changes within a length of time - say 5 minutes. Then I will give him only a kick for those 5 minutes to work with (with the tempo changes programmed). He will map out a choreography and I will film it. Then in my studio I will write the music to his choreography. Then I will take the music back to rehearsal and he will react with some changes. Then I film the dancers again. etc...