The first key to writing is to write not to think
The way you speak the way you write.
Like you can't speak without words, you can't write without words.
But, words will run away whenever you ask. Writing come naturally from the heart not the mind so, you can't write until you know how to feel.
At those times when you feel stuck, blaming your mind wouldn't gone work. Instead, you have to fetch your heart first. It's the main source from which your best words will show up.