Well, concentration usually stands for the ability to visualize and meditate. But it also stands for learning to not pay attention to bodily things and outside influences and thoughts that interfere with the process. I don't actually do breathing techniques much, i have shallow breathing, which is probably not healthy, but i still manage to accomplish things.
For me personally, I like to visualize the process of leaving my body, as in visualizing my soul, or whatever you call it, floating upwards, or sometimes visualizing appearing somewhere else. It works for me rapidly, but the actual process terrifies me at the same time unfortunately, so i never get really far, only about a few feet away, then i panic.
I think the process is different for everyone.
I've heard of lots of people, using the technique of visualizing themselves climbing up a rope. Doesn't work at all for me.
I am way too analytical to imagine climbing up a rope in a physical sense without my body.