My understanding is that it really is a very personal thing. I don't think you can do it wrong, per se, and I don't know that there's a standard. It's just about laying out very clearly what each person intends to commit to within the relationship. Did a quick search, and this seems like a fine example:
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.