Language

Human language can be the biggest stumbling block to effective communication. 

That might sound like an odd thing to say (especially since I am using human language to communicate these ideas to you at this very moment), until we realize that some of the most ubiquitous problems in creating effective arguments come when we carelessly use language. One of the biggest challenges, and perhaps the most important tasks, set before a thinker is to have a firm grasp on the language that you will be using. You should also carefully consider your audience; will they be able to readily understand some of the foundational concepts and technical terms you will be using? Tone, level of formality, correct word use begins the process. How much effort should you take in defining your terms? In the end, language is your only tool in written arguments; use it well and use it carefully. 

Audience

The first step is to decide who your audience will be. If you are writing a school paper, you will know exactly who your audience is. Hopefully, your instructor will have given you some feedback on style and tone. Your textbooks and other assigned readings might give you a clue as well. If not, I would suggest a serious tone, with a level of sophistication equal to the level and topic of the class. Obviously, a first year general history paper on the colonial slave trade will require a bit less of you than say a graduate level paper concerning some narrow topic in Kant's metaphysics. 

If you are writing for the internet, email or forums, you will probably want to take a slightly different approach. You might not ever know exactly who will be reading your work, so you have to make some assumptions and best guesses. Don't dumb down your arguments, though, just because they are on the internet. I would suggest shooting for a junior high reading level. Your tone can also loosen up a bit; make it conversational. A bit of humor interjected from time to time won't hurt anything as well. 

Whoever your target is, use the plainest language you can muster. There's no sense in working very hard on something and ending up confusing or frustrating your audience. Your readers shouldn't have to struggle to get your message. This is doubly important on the internet, as people tend to scan, rather than read, what is on the screen. Avoid jargon (or at the very least define your jargon) and complex grammar as much as possible. People tend to understand more when they are required to read less on screen. 

Tone

Without a doubt, how you use language is as important as the actual content of your argument.  Because a good portion of your personal credibility (thus your audience's willingness to listen to your arguments) depends on your tone, special consideration should be given to this area.

If at all possible, avoid provocative labels and lighting rod catch-phrases to express your passion.  

Definitions

Words do not have absolute meaning. This might sound like a statement too obvious to utter, but time and time again this problem crops up. Don't assume the definition you have in mind for a certain word is the same as your audience. Recheck any word you are not sure of. Have handy a current dictionary. It also wouldn't hurt to have an older dictionary on hand (personally I use Merriam-Webster 2000 edition and the Webster-Webster Online, Dictionary.com and the 1962 edition of the American College Dictionary). Whenever possible, define your term in text when you suspect that that term might be controversial or foundational to your argument.

Two fallacies of language use should be noted at this point. Equivocation and Ambiguity are two of biggest killers of solid arguments. Be sure you have control of the language you are using and mean exactly what you write.

General notes on language use

Of course, you should use the best grammar, spelling and punctuation you can muster. Though this is beyond the scope of this Web site, any good high school or college writing book should do the trick. Strive for consistency. Take your language seriously, because that is the only thing between your and your audience.