Window
Darkness is the absence of light. If you remember this, it will change your life. Changed mine. It is this concept that the practice is based on.
Any negative thought is darkness. How do you remove it? Do you fight fear or worry? Do you push or drown away sadness and pain? Doesn't work.
Instead, imagine you're in a dark room and it's bright outside. Your job is to go to the window, pull out a rag, and start cleaning. Just clean. And soon enough, light enters naturally, taking the darkness away.
It's that simple. Each time the mind shifts to darkness - fear, worry, pain, you name it - when you notice, clean the window. Light will flow in.