The quick way to draw and sketch you idea into concept art

The quick way to draw and sketch you idea into concept art down to sketchbook.If you have to many ideas inside your head, what is the quickest way to acquire ideas you have before it waters away.If you ever end with no ideas in you mind, where you don't know what to make- I have a lot of things in mind but have no idea on what should I do! First, Start with core idea first then narrow it down