It has definitely helped my mood and mental health overall to talk about the things that are on my mind, even if the conversations don't always end up going in my favor per se.
This probably seems super obvious to a lot of people, but it does not come naturally to me, and I suspect an equally large number of people have trouble with it too.
Painful to do in the beginning, but as people get use to your new truth telling ways, they learn to appreciate the honesty.
Chatting to somebody about the side effects of the antidepressants we're both on, namely decreased 'filter' when talking. Amusingly, said decreased filter might be one of the contributing factors behind this increased openness :)
Asking a friend who was obviously going through a hard time - "You don't owe me any answers, of course, but I wondered if you'd mind me asking whether you're okay, and what's going on for you?". Plus a lot of follow-up questions, phrased as "here are some things I'm wondering about, with absolutely no obligation to answer them; and of course if you have any questions for me, I'd be happy to answer".
Even just simple stuff like following up on throwaway conversational prompts - "hey, you mentioned as an aside that you'd done horseriding for fifteen years - that sounds like a big part of your life; how did you get into that?"
A lot of it's been about relationships, for various reasons.
However, I do have a couple of dedicated NVC practitioners amongst my friends, and a lot of other people who just use variations on those techniques without explicitly buying into NVC.
I've found that the principles behind NVC have helped me massively, even without formally being educated in it. I started using them a lot while I was navigating a very rocky relationship with a lot of arguments, and I guess the habit has just stuck - things like separating wants vs needs, talking about emotional state without using blame language, attempting to understand where the other person's coming from before replying, and so on.
I also set up a 'close friends' filter on Facebook for people I can be a bit more honest with - not 'all drama, all the time' type of stuff, but more about starting interesting discussions about stuff that we don't normally talk about: emotions, relationships, etc. I'm tired of keeping my Facebook life relentlessly positive and polished - not only is it bad for me, but bad for everybody else who sees me as just another person with a better life than their own.
It's all pretty terrifying, but it's definitely paying off. If you have mental health issues, I can't overstate the goodness of having friends around you who know and understand about that.