Working with a koan can make the world more transparent and alive and at the same time shift your consciousness in small and large ways. It's a work of art as well as a spiritual method and intended to be useful in your life and contribute to your happiness.
If a koan has grabbed your attention, then just let yourself be open to it at first. Maybe you understand it immediately. Good. What else is there for you? How does it enter your life? Maybe you want to take it deeper. Sit with a koan in your meditation and also let it accompany you wherever you go and whatever you do.
It's good if you can let the koan come to you. Reaching for it too much can push it away. When you let a sound, the sound of rain, the sound of a siren, come to you, the world comes alive. In the same way when the koan comes to you it makes the world sparkle too. Enjoy the connection with the koan. Is your heart open when you meditate with the koan? Let it into your body and keep company with your breathing. Let it get into your toes. You can become one with it, and then you might say that the koan walks about and goes to work and lies down to sleep at night. There is nothing you do that is not human and there is no place in your life too unacceptable or too boring or too painful for the koan to touch.
What states of mind appear? Think of them as belonging to the koan, not necessarily to you. Notice when you are judging yourself. Notice how that is. The koan is not judging you, but it does show you how much you judge yourself, and whether you live by winning and losing, praise and blame.
Whatever situation confronts you, let the koan interact with it. If fear rises, you don't need to force your way through; you can let the koan worry about it. If someone is yelling at you and the koan is present then the yelling might be transparent, and you won't close up around it. If your koan is Peach Blossoms, what's happening will be Peach Blossoms. If the koan is Original Face, then what's happening will be Original Face. The koan can transform your consciousness with amazing speed because it isn't involved with your ideas about what you can and cannot do. You don't need to make a case for yourself with the koan. It doesn't assume that you are a self.
The koan may take many of your thoughts and assumptions away. It may show you that you stand on an emptiness, a mystery. And you may find this freeing. When you witness things as they emerge from emptiness you may find that you too are just emerging. You too have no definite shape or identity and are essentially unknown. You are a something, vast and infinite, not limited by having a self. When you do not hold onto a set belief about who you are, many things are open and possible. You may also find that kindness just arrives by itself without effort. A few koans:
Yunmen said, Sickness and medicine correspond to each other. The whole world is medicine. What is the self?
A woman raised a goose in a bottle. When it was grown she wanted to get it out, without breaking the bottle. How will you get it out?
A coin lost in the river is found in the river. - Yunmen
Once Pang the layman was selling bamboo baskets. Coming down off a bridge he stumbled and fell. His daughter Lingzhao immediately ran to his side and threw herself down. "What are you doing?" he asked. "I saw Daddy fall to the ground, so I'm helping," she said. "Lucky no one was looking," said the old man.