As an ongoing practice I sometimes put a test on myself. For instance drawing white objects against a white background. I thought some pieces of garlic would be a nice challenge. It turned out to be less difficult then I was afraid of. When I looked close at the garlic, I saw all kinds of colours hidden in what I thought was a white surface. All I had to do was to exaggerate those colours to give depth and 'life' to the drawing.
Pen and watercolor.