After a few... events involving some newer forumgoers, I figured it would benefit everyone if there was some words of wisdom for newcomers to the forums, not necessarily the game.
Alright, so Rule 1: Don't mess with @GatoCommodore. He will dismantle you.
Ok seriously though, the forums can be pretty welcoming if you realize the atmosphere. People here are always welcome to new ideas and new people, should those new ideas be ideas worth sharing and new people be people worth listening to. However if you push the boundaries between constructive criticism and ranting, or outside-the-box thinking and shitposting, people are quick to notice. Not to say a rant every now and then is always harmful, it helps to get frustrations out, should you do it in a civilized way, nor is shitposting never fun to give a few LOLs at. But, the simple question you must ask yourself before posting something is "Does this make me look like an idiot?" Whether it be criticizing the game, or suggesting new ideas, if the post comes across as "rude" or "toxic" people are likely to give you some flames, regardless of who you are, hell ask @Nail he'll tell you.
When I rejoined the forums after taking a long, Overwatch-related, hiatus (and also losing access to my old account), I received pretty much no toxicity or naysaying. And that's because I was respectful to the intelligence of the people on here, and gave my ideas in a way that people could fairly criticize (granted I had a bit of an advantage having been on the forums before, but hey that's what this post is for). Sometimes it's better to just tell a joke on a post that you don't really know a lot about to alleviate some tension, rather than say something that makes you look stupid.
So TL;DR, ask yourself "Does this make me look like an idiot?" before you post something, and if it doesn't, post away.