How do you write the perfect song?

like i do a lot of composing and song writing, but i'm more modern rock based and its just put words and a melody line together with chords that sound nice. But I'm really inspired to write a really heartfelt song. And the message i want to portray is the same message as "Your Song by Elton John, and listening to it, it's just perfect, the words fit the melody, and the melody fits the chords in the way the message is suppossed to sound. How do you do that. If i could just steal the chords and melody of that for my song then i would, but how can anybody just write that, there must be a way to like, think ahead rather than use any old chord progression and any random melody...