DO NOT be loquacious in your writing, it is important to keep your subjects not too long, do not proliferate the amount of words in your writing to the point where you begin to ramble
Avoid using obloguy, using rude language is one of the biggest things to avoid in writing unless you are writing character dialogue or other scenario using that language. Another thing you want to avoid is using colloquialism, you want to be as proper as you can in your writing and using elocution is the best way to go when you are speaking as you are proper, formal, and well spoken.