Three main things- 1. Set a writing time each day. Same time every day you write. It will shortly become habit. 2. Just write your first draft. Don’t edit as you go, just get all the words out as they come. Your 2nd draft will be when you fix and organize what you’ve gotten down. 3. Stories go where they want to go. Start a story and just go with it. Once begun, you can think on the story at other times during the day, getting to know the characters and working out plot points.