Rapid prototyping is an essential part of every design process. You sit down with a blank piece of paper and jot down as many ideas as possible during a short period of time. Chances are you will end up with many designs that are too plain or too complicated. However, there will also be the excellent ideas born out of your creativity that you can build up on later.
Ramotion, a digital agency from San Francisco, posted a series of photographs that document the prototyping phase during their app icon design process. Their sketches are unusually detailed and beautiful, they allow the designers to create and compare many different versions of an icon before even launching Photoshop or Illustrator.
According to recent studies, drawing by hand can significantly improve your creativity so don't hesitate to spend some quality time with pen and paper!