most important is to come from a place of respect and to talk about the issue, not about the person. it should be about solving the problem together. never about pointing blame.

when i was still stuck in relationships that didn't work, most discussions were always about "who did (or did not do) what and why that was terrible". these days we talk about what problems we face, what we tried, how they didn't work and ask each other advice on how to deal with the situation.

i had to learn to be more humble and own up to my faults (that was hard). i also had to learn to reign in my temper when i was getting frustrated. (that felt impossible, but turns out to be easy when the discussions are not personally directed)

and another thing that has a huge impact on our communication: we validate, compliment or appreciate each others efforts constantly. we talk more about the good stuff than about the bad stuff, and that really makes a difference.

and lastly: allow each other personal space when needed

i know this is not really "new knowledge". every talk or tutorial about communication will tell you similar things. but it is what works for us.