Shoot exclusively in black and white for one month. If your camera has a monochrome mode, use it so you see black and white on screen while you shoot, not colour you'll convert later.

The purpose is to change what you notice. Colour is a massive source of information — and distraction. When it's removed, you start to see light and shadow, texture, tone, shape. Subjects that seemed interesting because of their colour become boring. Subjects you ignored become striking.