We've all been there. You've just come up with an "unbeatable" argument for your side and you're waiting for your opponent to admit defeat.
Then they reply and totally shred your argument, leaving you on the ground wondering what just happened.
I know I've stuck my foot in my mouth many times while arguing so I thought I'd put together a list of things to consider when I'm you're arguing with someone.
Preparing for the Fight
First off, don't try arguing a position that your opponent has authority over. Just like you didn't get anywhere by arguing with your parents about eating your spinach (if you did get out of eating it that was plain, dumb luck) you'll never get anywhere arguing about a pay raise with your boss or about a contest's rules with the guy who's running it. Their authority position causes them to see their argument as better then yours, so they will almost never concede a point and if they don't appreciate your argument their opinion of you will go down (think of your parents adding more spinach just because you argued).
Second, know both sides of the argument! The easiest way to stick your foot in your mouth is not knowing your own position. Resorting to "it's just commonsense" or "well, science has proven it" can become very embarrassing when your opponent asks you to back the claims up. Those statements may be true but unless you can prove their validity your opponent has no reason to accept them
You also need to know at least some of the other side's arguments. You need to understand their position before you can defend yours. If you don't know what they believe, you can't pick out the weak points in their argument and you're left arguing on their ground.
In the Heat of the Battle
Never let your emotions control you. This applies the most to face to face arguments, but it's still true about online arguments. If you don't keep calm and think straight, you'll say things that you'll regret later. If you find yourself getting angry take a break and come back to the argument later. You won't regret it.
This ties into the previous point: after you've written your argument, before you publish it, step back and consider how your opponent will read it. Are you backing up your claims with enough evidence? Is it possible for them to read it and think you're insulting or making fun of them? If they are an authority figure, are you making sure that they understand you're not challenging their authority? Miscommunication can cause a lot of problems.
After the Engagement
(That's engagement as in skirmish and not as in marriage, though this probably applies to that to)
If you've managed to convince your enemy to join your side, great! Most likely though, both of you still hold differing positions.
This totally changed my mind about bumper stickers!
It may seem strange to you that the other person can't see sense and agree with you, but remember they're thinking the same thing about you. No one likes to admit that they are wrong - that's just the way human nature is. If you ever talk to them again be nice and don't bring up the subject. Sometimes they have a certain concept of what the other side is like that you can help destroy just by being nice.
If they wiped the floor with you, step back and review your argument. Look for the places you messed up and work on improving yourself in those areas. Do more research on the subject so you're prepared for the next argument.
Conclusioni
(^ that's just a Google Translation into Latin to make me appear smarter)
I hope you find some of these tips useful (and yes, you could argue whether anybody could find them useful but please don't...) Have fun arguing!
Don't raise your voice, improve your argument." ― Desmond Tutu