Ones to really watch out for IMO are Appeal to Emotion and Ad Hominem. These two are the most used fallacies in internet debates IMO. The more you familiarize yourself with these, the better you may become in recognizing a poor argument.
And if you're going to call someone out on a fallacy, don't throw it down like a trump card. SHOW how their argument is fallacious.
Personally, I think cognitive dissonance is a major problem. People in general have opinion set A at any given moment, and when a direct contradiction to one opinion in set A occurs, they either fight it, or flee.
There's a lot of science behind the idea that most people use their reptilian brain in arguments, emotionally defend their already engrained views, and then try to logically defend it after the fact.
The real challenge is while defending your own views, to try and attempt at discerning whether or not you are simply emotionally responding to a cognitive dissonance, or whether you are rationally defending a built up worldview with foundations in knowledge and insight.
I'd like to say I do the latter, but I'm sure everybody would like to agree with that...