I just thought I add to this one, in regards to point 6: not writing a track around a melody.
I find it best in the writing stage to write many aspects of the song quickly, then flesh it out into a full arrangement later. I'm a pianist and I almost always write by making a recording (on my iphone) with myself playing to a metronome, playing chords with my left hand and melody with my right. This gets down the rhythm (in an extremely limited fashion), harmony and melody. I'll then make a note of what instruments I will use. Then finally I spend some time in front of the DAW and make the thing.
Writing from a drums and bass seems very strange to me. I tend to think of what emotion I want the piece to convey. Melody and harmony are the most effective way to reach this.
Thank you guys, I've learnt so much from this thread:).