When doing Na, or sensitivity training, you want to go slow and try not to compete but to be a good partner. Close your eyes and learn to sense with the skin on your hands. Go slow and start with one hand at a time and over time move to two hands simultaneously. Once you are comfortable with the physical movements then try visualizing your lower energy center while practicing Na. After that, work on the visualization of the 4 gates breathing while practicing Na; you can start with two gates, the upper ones, and over time add the lower ones as well. When you advance even further, you can do Na training on two wooden blocks (still visualizing the lower energy center, of course!).
Like the Yin-Yang, Eastern Martial Arts and Western medicine are two halves of a whole my mission is to preserve the ancient mind-body tools, and pass them on to you.