
My opinion has always been this: there is no particular best way to write a song. That’s true in all of the creative arts: there is no process that is necessarily better than any other process.
Having said that, I will add this: the fragment that you initially create — whether that fragment is a chorus hook, a line of catchy lyric, an enticing bit of melody — will tend to get more attention from you than all the other bits you write.
There are many roads that lead to a finished song and there are as many variations of the songwriting process as there are songwriters in the world.
Any way is the best way to write a song…
Source: The Best Way | The Essential Secrets of Songwriting