If you're working on a project and get to a point where you just can't figure something out, or can't get the next idea, do what Sherlock Holmes has done: Leave the project and do something completely different. Go for a hike, see a movie, visit a friend, and so on.
When attention is too tightly on something as a way to find a solution, we start to block our creativity. Taking the focus off the project by doing something entirely different opens the channel again.
Give the subconscious opportunity to work for you by coming up with solutions while you do something else.
Sherlock Holmes tended to go to the opera :-)