Iñigo Quilez (rgba) has some awesome rules for making 4k demos; the rules aren't that different from making a game, or other kinds of art for that matter:
- Get some interesting effect(s)
- Play randomly with all the parameters to get used to them
- Think about something interesting to do with it (find an idea?)
- Synchronize it to the mzk
- People will think there is an underlying concept
I like the fifth point, it makes demo watching like cloud gazing; a kind of canvas to project your own imagination onto.