What are the steps and please share your experiences working with him
I had/have the intention of invoking and maybe being possessed by him, still not did so but anyway you may either practice only that:
Or insert this invocation
before calling Metatron by gazing at his sigil and repeating the conjuration.
Further elements may be added, such as beginning with Greater Ritual of the Pentagram, Watchtower, Bornless Ritual.
I think the book ‘Archangels of Magick’ has a ritual for it.