If you suffer from "writer's block" or feel that you are too busy doing stuff right now to think of new ideas then you will like this early 90's video with John Cleese.
In it he looks at how to get yourself in a zone where you are open to ideas. To paraphrase his 5 steps...
1 - Space. Cut yourself away from the emails and phones.
2 - Time. Give yourself time to ponder the issue - an hour and a half is best.
3 - Time again. Do this on a regular basis.
4 - Confidence. This must be a risk free environment. So expect to go down dead ends and make 'mistakes'. It is all part of the process. It is close to how kids play; freeform and willing to go in any direction.
5 - Humour. Have a laugh. Jokes often come from joining two different meanings and forcing the brain to make new connections. This is the same for new ideas. Working together can help - but pick good 'play mates' who are up for this way of working too.
Good stuff. And balanced out by his call to not do this all the time. You need hard graft too.
Lastly, there was one phrase in there that I liked was the "Intermediate Impossible". Most of the time we work through a problem where each stage of thinking is solid, it makes sense. But we should challenge that methodology. Sometimes you can leap frog to a better idea by having a stage that doesn't stand up on it's own. It is too crazy. But it helps you get where you need to go.