I don't think there's a secret.
I've been banned three times and I really can't figure out why.
Ban 1: A guy made a thread asking for help with transmitting certain video formats from his Mac to his television. The first or second guy to reply said something along the lines of "I'm glad I have a PC with HDMI. I don't have this problem." I was new to Gaf, so I made a criticism of Apple for not including HDMI in their computers despite my low quality netbook having one. I was called out on the statement by someone saying that I "should take that crap out of here. This isn't the thread for that." I was somewhat puzzled because he didn't call out the guy who said he was happy he had a Windows PC with HDMI. But I immediately apologized and edited my post. Still got a 3 week ban for it, though. It would have been a month, according to the mod who banned me, but luckily my quick edit knocked a week off.
Ban 2: A user made a terrible thread about men in the US being raped more often than women. His link led to a non-credible article with non-credible sources. I knew it was shitty at first sight. I made a post saying, "I can't wait for _________ to see this," referring to a user well-educated on the topic and passionate about it. Unfortunately, this post backfired because said user felt upset that I did this. I was banned for three weeks. Funny thing, since making that post, I've seen more than half a dozen like it mentioning the same user in various threads. I was, needless to say, very upset because by this point I felt like I was being unfairly picked on by mods.
Ban 3: Made a comment about the strength of biological bond between parents and their biological offspring. Compared that bond to the bond shared between adoptive parents and their adoptive children. Made this comment in a related thread, in a related way, wasn't rude, didn't push the point, didn't make up anything. Banned for two weeks for making "hurtful statement."
In short, there is nothing you can do to avoid being banned, and by extension, probably nothing you can do to avoid being perma-banned. Chances are, one day you will make a comment that you believe is entirely relevant to a thread, civil, non-demeaning, unhurtful, scientifically supported, etc... and you will be banned. The mods are charged with using their own discretion. They're humans, they're not perfect. When I first got approved for Neogaf and was allowed to post, I never dreamed I would be banned. "Nuh-uh, not me," I thought. The only people I had seen who were banned had posted clearly inflammatory statements with no other visible purpose than to offend. So I thought it would be easy to not get banned as long as I remained relevant and polite. Unfortunately, it doesn't work that way. And nowadays I see plenty of posts that I think are ban-worthy but the posters get away with it.