Become nothing. Say what? I don't mean nothing in the sense of being unimportant, or worthless, but rather in being not so full of yourself. When you can envision yourself as nothing or no one thing, then you make a lot of space for God who is everything and all things. You can call this "All" whatever you want. It is not you in your self-importance or self-focus. Don't take up space in your head or imagination. You will bump out the True All. Meditation is a way to separate just enough from your "allness" to allow for the True All.
As I age I find that I forget a lot of things, but I never seem to completely forget about my "selfness." Inside my head it is hard to stop thinking about me. I am clay but think I am the potter. I meditation I allow myself to be me, clay, and let the potter go to work. Something beautiful will happen. It is always in the clay, but it needs a potter.