You discover them the easiest by visualizing a vacuum cleaner hose that you first suck up close to your skin. Sometimes you notice bumping into something metallic. That way you activate your astral vision before moving inside. Then you move it inside yourself and continue.
I do the Cleansing rite of the Goddess and the Cursing rite (with Babalon) from Petrucelly´s The Black witch nowadays. It actually gets easier to breathe when you see the shining pentagrams around you.