For those who work well with visual imagery, have a look at this adaptation of one of my clever student’s drawings. The mid-point of the “8” represents your lungs as they are when speaking normally, just havin’ a conversation. Michel Debost calls this “mid-breath”, and describes its usefulness in his book The Simple Flute. The white arrowsheads, hopefully discernible on your screen, show the flow to and from this mid-point.
I love how the figure “8“, when turned on its side, also represents infinity.
Once you pass this point by actively filling or actively emptying the lungs, it can be helpful to realize that the next natural step is a passive one. I find this helpful when having to take a quiet, quick breath when playing, say, a fast movement from a Bach Sonata.