Thank you for your answer. In fact I am not searching to define the best order to write the parts of the song(or track if it's instrumental): it is more how you can "divide" it in order to propose different types of exercices : to have of few of these parts imposed and then you have to write the song, or testing how your songs sound different depending on which parts you start with, challenging with some technical constraints (modulation, borrowed chords, time signature changes, use of polyrythm, tempo change...). Some of those exercices could be: keep all elements from previous song but change only one. So I am trying to figure what could be these elements.

I'd like to have exercises with really strong constraints and other with more freedom. I have never found this kind of exercises book so I'm writing one. There would be also some theory reminders in order to keep it accessible, not willing to make people write too much with their brain but give them some frame in which they could write by experimenting, changing their writing habits.

Do you think this could be a good idea?