In case you were wondering why we tend to be so harsh on the subject of grammar, it is because a properly written post shows that you pay attention to and care about what is coming out of your keyboard, rather than just blurting out whatever half-formed thought tumbles into your head at the moment. It also shows respect for the people who read your post. A lot of people are poor typists or bad at spelling, so they drop their posts into Word or OpenOffice and give it a run through the spell checker.
That said, on to the advice.
When in a controversial thread, READ THE EXISTING POSTS BEFORE POSTING YOUR OWN RESPONSE. Often the point you want to make has already been made and discussed/fought over. Posting without reading just reignites dying flames and extends threads that are already painfully long and repetitive to begin with. Also, before you respond with something you think is playful or satirical, read it to yourself in the most obnoxious, aggressive, snotty way, and then be aware that there is at least one person in the thread who will take it exactly that way. Then edit your post with that in mind. I'm not advising self-censorship, I'm advising you to be aware that on the internet, no one can hear you tease.
Some people take public pride in their post counts. I suggest you take private pride in your read counts. In real life, would you jump into the middle of a conversation between people you don't really know without making sure you knew what they were talking about? No? Then don't do it here. It's just as obnoxious as it would be in real life, and much more destructive to the discussion because they can't simply pause, glare at you, and resume the the conversation.
If you find something overtly offensive or believe someone to be a troll, hold your tongue and hit the report button. If you have concerns or questions about the moderation of the site, PM the moderators. Do not complain about it in public. Remember that while this forum is open to the public, it is privately owned, and as any one of the many libertarians on this site will tell you, the people who own a thing have the right do whatever they please with it, including banning the whiny asshats who feel the need to post threads picking fights with the mods. Your right to free speech applies to your blog, not this website. You are in someone else's house. Show respect.
Don't take things personally, especially the personal attacks. This person does not know you. Their opinion of you is just that. The rest of the forum recognizes this. Also, consider trying something innovative and unexpected--when someone calls you on your shit, consider that they might be right, ask them why they disagree with you rather than becoming reflexively defensive, and DO NOT RESPOND WITH PERSONAL ATTACKS OF YOUR OWN. If they were jackasses for insulting you, why would you want to join them in their jackassery? Why lower yourself? The Escapist forum members pride themselves on rising above the general level of internet discourse. Prove them right whenever you can.
I guarantee that there is someone on this site who thinks your beliefs are stupid, your worldview is deluded, and your opinions are worthless. I guarantee you will come across this person if you spend any real length of time on this site. And the chances are, this person is one of many who will jump all over you when you try and defend your beliefs. As a personal example, I am a self-identified feminist, which means that, as such, I have been and will be blamed for everything from the death of chivalry to the miserable breakup of someone's last relationship. OK, then. It makes me angry, it hurts my feelings. I just have to suck it up and respond with dignity rather than flames. Or--here's a thought--walk away. And this will happen for Christians, atheists, conservatives, liberals, gays, homophobes, Americans, libertarians, socialists, people who voted for Obama, people who voted for Bush, people who play Halo, and people who play WoW. Prepare yourself for this and deal with it when it comes.
Conversely, I guarantee there is someone on this site who agrees with you and does it so badly, with such vocal and persistent idiocy, you will be reduced to chewing on your keyboard and pounding dents in your desk with your forehead. There is a very good chance that this person will be harder to deal with than the person who totally disregards everything you hold dear. Again, prepare yourself for this and deal with it when it comes.
This is a very lively site, with lots of smart people who have strong opinions and a lot of time to post them. In detail. Many, many, many times. This will be one of the reasons you stay here, if you do stay here. I hope you do. The fact that you actually asked for advice on how to get along here speaks well of you in my opinion. Welcome.