I start with very short pieces, usually no more than a handwritten page. I try to focus on something specific: a person, a moment, a place. I do what I ask my students to do when I teach creative writing. I explain to them that such fragments are the first steps to take before constructing a story. I think a writer should observe the real world before imagining a nonexistent one.In Other Words, Jhumpa Lahiri. pg 61
Many of the exercises Jhumpa describes for learning how to write in Italian can be used for improving your writing in English.
Start small. Start by filling one page.