I know you've written your share of poly fic, so I was wondering if you've done a lot of research on it--and, if so, could you maybe share resources/words of wisdom?
Hi, anon! There are two ways for me to answer this question, and I'm not sure which you want? So I'll do my best to do a bit of both.
Big disclaimer here: I am not an expert. My research, such as it is, is writer research, and often it's been remembering posts that have crossed my dash. If you are considering a poly relationship (which is the first of two ways I interpreted the question), you are probably going to get more useful information from online research from people who are experts. The first two potentially-useful resources that came up in a quick search were the Polyamory Society and More Than Two (More Than Two in particular seems to have some handy PDFs). There are almost certainly many many resources a google search doesn't give.
If you're asking about writing poly, I can probably be a little more help (though I reiterate my disclaimer). There are two things that I try to stick close to in whatever poly I write: the first, by far and away, is communication. Everyone talking about what they want, everyone making sure they get it, everyone checking in and reaching out. Relationships are hard enough with two people communicating, and with three or more it becomes super important. Even if you aren't as into writing Talking About It Porn as I am, the characters all being explicitly on the same page is good. The other thing I try to do, especially if I'm going for an equal triad (which is by far the most common kind of poly I write), and especially in fanfic, is develop the side(s) of the relationship that aren't developed as much in canon, or that don't make themselves most obvious. A lot of poly in fandom comes from two people having chemistry with one person, and that's great, but I like to make sure that Courfeyrac and Cosette, or Freya and Arthur, or Eliot and Parker, specifically get development. Otherwise it feels lopsided to me.
If I answered the wrong question, or if you want my answer on one or the other of the questions I /did/ answer expanded, please feel free to come into my ask anytime, on or off anon.