i always start with the main theme or the message i want to impart to my listener. that way i don't really box myself into a specific flowchart which causes a lot of mental block. some themes/messages would be better off started with a melodic hook for example, some would be better off started with a beat, a lyrical hook, a guitar riff, etc etc i always keep my options open so i can flow more freely in my writing. if i had to force myself to always do lyrics>chords>melody>beat or any other specific flow, it would really hinder my progress and stunt the potential of the song i'm working on.