If you can write well, people will assume you are smart and qualified (even if you're not). The reverse is also true: if you cannot concisely articulate your ideas, no matter how ingenious those ideas may be, people will discount them and assume you are less intelligent.
Some people have a difficult time putting pen to paper. I chuckle every time I think about a comment someone once made to my mother. He said, "I can read writing, but I can't write reading.'" I suspect a lot of people feel that way about their own skills.
I am very fortunate in that writing seems to come naturally to me. Nevertheless, there are some things that I think have helped improve my own writing. I thought I'd share them.
Writing is a skill, and like any skill, it will improve with experience. If you push yourself a little, you'll find that the more you write, the better you get. Indeed, one of the primary reasons I started blogging two years ago was to give me a reason to practice my writing. Looking back, I think my writing has improved since my original post.
Stretch Your Vocabulary
According to one study, the average 12th-grade student comprehends between 60,000 and 100,000 words. Unfortunately, most people only use 5,000 or 6,000 words in their own speech. I've seen other studies that statistically paint the same picture, but in this context the meaning is the same: people understand more words than they actively use.
For a writer, this means you have a library of some 80,000 words (on average) that are available for you to use in your writing without becoming overly verbose. These words add flavor and detail; they describe subtle nuances that would otherwise be unknown to your reader. Why constrain yourself to less than 10 percent of that?
I find that as I write, words often come to mind that appear to be appropriate for what I am describing. When I'm not sure, I look them up. Sometimes I find that my initial instinct was correct. Other times, I find that I was wrong about what I thought the word meant. In either case, the process of looking up the definition cements the word as part of my usable vocabulary. Also, never underestimate the power of a good thesaurus when you can't seem to find that perfect word to describe your topic.
Writing is more than just the mechanics of grammar and syntax. To be effective, writing also has to have style and flow. Reading things that other people write can help you define your own style, and assist you with intuitively determining a flow. To be a good writer, first you have to be a good reader.
I haven't written a sentence yet that didn't benefit from a good proof-read. Or a second, or a third proof-read for that matter. When I finish writing anything, I always go back (usually several times) and review it. Sometimes I focus in on one particular section, but I always finish by reading the whole thing from start to finish so I can verify that it flows nicely.
Consider Your Audience
I think it helps to visual the type of person who will read your writing. Are you writing a technical paper, a human interest story, or something you think children will read? Are you trying to write more formally, or more casually? Is humor appropriate?
Avoid Profanity and Slang
I'll be the first to admit that having spent 7 years in the Army, I can swear with the best of them. Try to keep in mind that there are very few venues in which written vulgarities are appropriate. Again, the idea is to leave a favorable impression. If you use excessive obscenities in your writing, people will draw the conclusion that you have a narrow grasp of written English. From there, it isn't much of a stretch to conclude that you are less intelligent.
I sometimes chuckle when I come up with something I think is really witty. To be honest, I think I'm tickled as much by the thought of someone else enjoying it as I am with my own originally quip. As you write, imagine the reaction your readers will have, and try to have a little fun with it.