The "I am" focus.

A lot of people spend years trying to figure out what the "I am" focus is all about. Nisargadatta mentions he spent three years or so focusing on it, and was liberated. Others have talked about it, via self-inquiry, Gurdjieff work, and even through Zen kian use.

It's really nothing more than going back to the idea of focusing on one's apparent personal sense of self, consciousness, wakefulness etc. Just the sense of being awake that happens every morning as opposed to deep sleep or unconsciousness. It's like focusing on the TV screen rather than the images, assuming we were a TV set. 

The practice is very simple. Sticking with it for days, weeks, months and years is the hard part, and VERY few have the tenacity to do so- hence Nisargadatta's insistence that only a few in a hundred thousand (later revised to a few in a million) would really understand it and arrive.