I. If someone insults you, you don't have to retaliate.
So some anonymous bozo doesn't like you - so what? Learn to let it go. Hurling insults back only makes you look like a complete idiot.
Do you ever see this scenario? Troll insults Johnny, and Johnny argues with Troll, trying to prove Troll wrong and get him to apologize. Eventually they just end up flinging variations of "your mama" at each other.
It's fruitless, obviously, because trying to get a troll to be logical is like trying to empty a bucket with a soup strainer. So all that happens in the end is that the troll is still a troll, and you end up looking like just as big a jerk as he is.
Let insults slide off your back like water off a duck. (Two water metaphors and it's only the first tip, wow!)
II. Sometimes a critique is just a critique.
Some deviant critiques you, and neglects to point out all the positive qualities in your work. Don't assume that it's because he was trying to be rude. Perhaps he just didn't see any positive qualities that stuck out to him, or perhaps someone else had already pointed them out and he didn't feel like giving empty compliments.
Most critiques aren't attacks, so learn to just take them into consideration and don't take them personally. Even if they seem unduly harsh, it's a safe bet that the commenter doesn't have a personal vendetta against you. (However, if a critique is an attack, Rule #1 applies.)
III. If you see someone has stolen art, report it and move on.
Getting up in someone's e-grill and telling them "Hey, this is stolen and I just reported you!" is about the dumbest thing you can do. The best possible situation that could arise from doing that is this - they take the piece down, and put it up again a week later. In a worst-case scenario, an all-out journal flame war begins.
There's a cool little "report deviation" button. Use it and shut up. You don't look like a hero or a vigilante or a good samaritan by attempting to warn the perp of an impending banhammer.
IV. Don't call people out in your journal or anywhere else.
This goes back to #3 - don't engage in a land war on deviantArt. By land, I mean your journal, which goes out to EVERYONE WHO WATCHES YOU. If you regret it later, there's no taking it back. Argue in notes if you have to, but the minute your dirty laundry is in print, you're asking for a shit storm, and it's rainy season.
V. Don't "leave" and come back.
I don't care how upset you are. The minute you make an angsty "leaving forever!" journal, you lose the respect of your watchers. It's a ten to one chance that you'll come back and answer comments and then decide not to leave after all after seeing the "overwhelming support" - aka, the token affections and pleadings from the innocent fans you've duped. Congratulations - you're pathetic!
If you're thinking about leaving, just do it. Don't make a big dramatic exit. At least that way you'll be remembered fondly.
VI. "Spreading the word" does NOT help.
This relates to #4 and #5. You might think you're being an awesome friend by "warning" everyone you know about an art thief or a troll, but in reality you're just getting yourself, and potentially everyone who comments on your journal, involved with said troll/thief. If you just keep quiet and keep your nose clean, there's less to worry about. Feeding the flames only causes MORE trouble with the guy.
The golden rule is report, report, report. Make sure he gets what he deserves, but do it quietly.
VII. If you get wrongly accused of art theft by a deviant, don't react at them.
Show your proof to the proper authorities and brush it off. You don't need to get angry at the person - for all you know, they could have genuinely thought it was a stolen work.
Actually, it's a compliment. Someone thought your work was so good that they assumed it was stolen! Perhaps your work was hosted on your other site, and they simply didn't realize you had multiple websites.
(Or, of course, your work might look WAY too much like another person's, in which case you should probably think about why that is.)
VIII. Don't lead (or be part of) a torch-and-pitchfork brigade.
If someone steals your art, spams your page or insults your mother, don't call all your little watchers together to flame them. They're your friends, not your flying monkeys, and while most people have good intentions, they are also far too eager to be part of a mob. It's just human nature.
Nothing good has ever come out of being part of a mob. At best you'll earn yourself a blurb on Encyclopedia Dramatica and everyone will think you're a lemming, a fanboy/girl or a brown-noser. If you lead a mob, the consequences could be more severe.
IX. Take things into perspective.
This is deviantART. Is it really worth getting all worked up about? Try to imagine yourself ten years from now - would your future self look back on how you're acting now and roll their eyes?
If you want to be successful selling your work online, do you want your past to haunt you? Do you really WANT a bunch of enemies, or do you somehow think that time will wash away all the traces of your idiocy? Think again. The internet is forever - everything you say on here will never go away.
X. Pitching a fit only works in restaurants.
Don't spam the admins with notes demanding that something be done about so-and-so. Don't threaten to "cancel your subscription" or leave or write a nasty thing about dA on your xanga.
Trust me, no one gives a flying crap if you do. This website is massive. For every second you spend writing an angry letter, seventeen and a half billion people join up. And only like 75% of those are plz accounts.
This isn't Applebees - no one's going to give you a coupon for free jalapeno chipotle asspoppers if you're upset. All it accomplishes is pissing off the admins.
I hope these tips are helpful to someone.