There's a saying that the more you do, the more you can do. This is why it's important to practise writing every day, if possible. You don't have to actually get words on a page, although jotting notes down will help to take your thoughts further, and give you something to come back to. Playing 'what if?' using characters you see in the street, topics that are in the news, conversations you overhear and situations you come across all serve to get your imagination moving and the ideas flowing. Have you read a thought-provoking book? Play 'what if?' with it. See a strange headline in the newspaper? Play 'what if?' In fact you could try putting a few random headlines together.
When you get tired of 'what if?' you can move on to 'consequences'. You pull two random characters from a hat, a random setting, he said, she said and the consequence. Okay, you might end up with unusable nonsense, but you might have the start of something off-beat, original and intriguing, and having trained every day, you'll be alert to the possibilities, and ready to make the most of them.