I've been thinking for a long time about tips for commenters. Just basic stuff. I know it sounds a bit conceited, but the rules that we take for granted are not always understood, particularly when someone is new to the habit (and we can safely call it a habit as much as anything else).
1.) Use proper grammar and punctuation. It helps people take you seriously. There are resources beyond count for this on the internet. If you have a question, it won't remain unanswered for long. Also, when you can, provide links for sources cited.
2.) Reply to others as often as is prudent, particularly when you have something positive to say. Whether you know it or not, you are contributing to a community, and people enjoy positive feedback. Acknowledge the contributions of others.
Pay it forward. If you have received lots of praise for your comments, remember to spend some time in the gray section promoting smart and entertaining comments. Even writers such as Morning Gloria came from somewhere and succeeded, in part, because other commenters encouraged them.
3.) If you receive negative replies, try to address the substance of the criticism rather than the ad hominem attacks. Trolls and assholes lose steam when you don't engage. In fact, one of my tricks to responding is keeping a reply to a mean response short and simple. Don't waste your energy crafting a long, detailed response for someone who just wants to drag you down into the dirt.
I do tend to distinguish between negative comments and trolls. People are welcome to disagree with me, but I draw the line at anything that approaches a direct insult.
4.) Delete replies that are truly mean and/or trollish. Garbage-filled comment sections lead to low morale and open the playing field to an increasingly ignorant and uninformed commentariat (like Youtube).
5.) Read both the thread and the full article before commenting. This will prevent you from drawing incorrect conclusions and from repeating opinions that have already been given for the nth time.
This is actually a huge fault of mine. I have frequently rushed into the commenting section without fully reading the article, and it reliably leads to my embarrassment.
Also, remember that news blogs such as Gawker benefit from sensationalism. It's in their best interest to provide scandal, but when you dig into the sources cited, links to newspaper and other blogs, you often find that Gawker has not provided the full story. So read those links if you can.
That's all I can think of for now. I'm pretty sure I missed a bunch of stuff, but I wanted to open it up to other suggestions.