I do not think you are a good writer if you know how to write.
As you are not a good musician if you know how to play or a good painter if you know how to paint.
A good writer is somebody who is able to write what the others like to read.
Well or badly written it doesn’t matter too much.
It matters how you tell the story.
It can be a long story or just a few lines.
A good writer is the one who is able to make a picture.
A picture that the reader can see and likes to look at.
A good writer is somebody who tells a story from an interesting point of view, is the one that gives you, with a few words an idea of what he wants to say, or better, of what he sees and feels.
Writing is the way of communicating with words, like painting is communicating with pictures and colors and music is communicating with sounds.
Let’s imagine there is a woman with a red dress and long curly hair.
Number one will just say: there is a woman with a red dress and curly hair, this tall and this thick and so on...
Number two will say: in the middle of the crowd I saw a woman in a red dress, her hair was curly and shining in the sun light...
Number three will say: I had a glimpse of red and a feeling of déjà vu.
I saw a woman in a red dress and it was like a memory hidden in my soul becoming real, a glimpse of red in a big crowd.
I was twenty again and it was the first day of Summer...