Re: How to write a …
Peace teelobhain
Not exactly a person with a lot to say are you? 
Sadness comes in many forms about many different things you need to explain what they are and some story that made you sad. Then this can be played on.
Use metaphors such as dark cloud to represent sadness and it will follow that the rain or shadow produced by this cloud are products of sadness … rain being tears and shadow being gloominess or loneliness.
Sadness can be a burden so playing on the idea of heavy laden clothes drenched, coldness, bitterness, pain and other offshoot concepts should be exploited. Icy winds - poison - barbs are metaphors for the offshoots.
So let’s say that a personal encounter with someone made you sad because it brought back old memories of a distant love … then this can be the theme of the song … All of this is part of the planning process.
You need to decide next on the style of beat and rhythm and make it suit the theme.
Then you need to construct much like poetry the words. Make up a chorus it is often easier to do this just after the first verse and then prepare the other verses.
In our example above we can say:
Verse 1
Haunted by a distant memory all I see is you
You’re a curse that stops the sun from coming through
Shades of grey and black that is all I am to them
I want to sing a sombre tune, can’t care less if they condemn
Chorus
Dark cloud, O dark cloud you’re my only friend
He crushed my only pearl that I still cannot mend
Dark cloud, O dark cloud pour for me once more
Intoxicate me in your shadow and I will lock the door