Getting the ideas out of your head and visible either in 2D on paper or in 3D sketch models. Once the idea is out it can be talked about and refined.
The threshold test for quality is simple: Can someone else understand your idea?
Visualising ideas will make them easier to understand and modify, and will in turn stimulate new ideas.
Any 'mistakes' you make will become the portals for further discoveries.
Sketch ideas as a response to a stimulus like a brief, or product analysis, or listening to music, or taking random words or images and incorporating them into you design process. The drawings don't need to be perfect: they only need to have just enough detail to communicate the idea. If you find the drawing or model doesn't match what's in your head then add words to explain.