1. Fallacy orgyKnowing about argumentative fallacies is important. It helps you to see when flawed arguments are used against you and it saves you from falling into a trap of thinking you have lost. However accusing someone openly of a fallacy can be a grave mistake. Many amateurs will not know what a fallacy is, and then quickly look it up. They will then deny the fallacy and accuse you of a fallacy every time you comment. Most of the time they are simply misunderstanding the fallacies. When both sides engage in this the entire original argument gets lost and the whole conversation devolves into a meta argument about what fallacies are. I have found it much more productive to describe the fallacy and why it is flawed without even mentioning the word fallacy. Beginners can understand this kind of reply. I have even been accused of a fallacy fallacy. Turns out they were committing a fallacy fallacy fallacy. Wow!
2. Assuming that your facts are rightThis one has bitten me more than once. I read something a while back and the information has rotted in my brain. My numbers are all wrong and that makes it seem like I am lying. Not only that, cognitive biases tend to cause us to remember larger quantities of things that favour our positions. It is always better to check a fact before using it, because a fierce opponent will try to use any inaccuracy to discredit you entirely.
3. Not conceding points when you are wrongIf you know you are wrong you should say so, because your opponent can then adjust to your renewed point. This is especially true if you make a mistake. It is okay to make mistakes. It doesn't mean you lost the entire argument.
4. Not agreeing with things because of who said itSo your opponent says something true but because you are against them you argue with them. You don't realise that you agree with them because you are reading their points as if everything they say will be a polar opposite of your ideas. This effect is much more subtle than it seems, and I have noticed by carefully rereading points made by my opponents that I actually wasted considerable time trying to argue against something I agreed with.
5. Trying to winIf you are arguing to win then I don't want to argue with you. If you are arguing to find the truth I am willing. People who argue to win have made their conclusions prior to even starting, and the irony is lost on them of engaging in an argument when nothing will convince them that they are wrong.
6. Taking abuseBecause online argument is not moderated or controlled some people you argue with will abuse you and insult you. This tends to piss me off and soon I am too emotional to give any reasoned responses. It helps to let them know that you are angry and that you would like to be treated with respect. Don't hold back when expressing your feelings. Feel free to call them names back. You should always keep the high ground when making points, but when you draw the lines of what is acceptable you can be colourful and emotional. After all we are humans arguing. Humans have emotions and that requires mutual respect. If you can't get someone to respect you, refuse to continue arguing with that person and if it persists then block them. We need to spend our limited time wisely.
7. Using fancy ass languageI like english. I like big words, but some people take it too far. Plain old english would do just fine, but they use uncommon words that need to constantly be looked up. Often when I do look up the words they use I realise that they have used them in error. I never mention it to them unless the meaning is so wildly different as to make inference impossible. Fancy words in my opinion should be used in moderation, not only because not everyone is a native speaker (I am not a native speaker), but also because an overdecorated sentence can be hard to read. Misunderstandings shoot up and frankly if you keep using fancy words everywhere you look like a pompous asshole.
8. Assuming that everyone is like youSome people seem like they start arguments in the middle, all their premises are considered by them to be self evident to everyone else. This results in a constant Q&A trying to figure out how they got to their answer. Show your work! Other people don't possess the same knowledge you do.
9. Check yourself before you wreck yourselfBefore bringing up points of argument with others do yourself, and them the favour of arguing with yourself about it. Imagine yourself in their shoes, and try to come up with the best arguments refuting your position. This saves you from making the mistake of thinking "Ah that one is brilliant. I will use it!" and being made to look dumb when it crumbles under scrutiny. This is a hard one in an unprepared debate, and most internet debates are unprepared.
10. Don't assume your opponent is wrongProbably the most important thing ever in any debate. Be willing to fail, and constantly try to understand the points that others make. If they are really right and you are wrong you need to find the path to the truth as quickly as possible, and not waste time assuming they are wrong without seriously considering their position.
Yup...A lot of this stuff works best if both sides of the debate follow the rules. You should still try to follow them though even if the other side doesn't. I know it hurts when you are being polite and conscientious and the other side is insulting and fallacious, but holding the high ground is always better on principle, and your character will eventually influence how seriously you are taken by others.
Good hunting folks!