1) If you're an Lucid dreamer you can take ideas from them dreams; that's what I do. If you don't know what a Lucid dreamer is, it's when you are conscious when dreaming and can control how the dream develops (you are awake within a dream)
2) You can't get ideas from songs or memories or pictures, what I mean is that look at a picture or song lyrics and write about the e.g. Taylor Swift - Love Story is about Romeo & Juliet...do u see where i'm coming from?
3) You could basic it round you're life but never anyone else unless they let you
4) You never know perhaps one day a story line will just come to you
Hope you got some ideas from that & have a great day
Sky xx