Few of us speak as eloquently as we think we do. We interrupt ourselves; we repeat ourselves; we use generic words and make unclear points. Natural speech is full of artifacts that don't make for compelling speech, much less effective writing.
If you want your writing to command respect, ignore the conventional advice and don't write like you talk. Instead, master conversational tone.
"Conversational tone" is the deliberate use of personal language that appeals to the casual reader. An important writing technique, it mimics how we believe natural speech should ideally sound - dramatic, confident, empathic, intelligent. It is new-and-improved natural speech, polished to a shine and missing all the embarrassing parts. Conversational tone is formal language designed to look informal.
Most professional writers have discovered that conversational tone is neither natural nor magic, but a carefully crafted illusion. Use these tips to create that effect the way the professionals do it:
Follow the rules. While no rule is ironclad, formal grammar matters. You risk looking illiterate if you ignore established grammar, punctuation or capitalization rules. Conversational tone is only window dressing; follow strict formal construction guidelines for any writing that represents you professionally. (Professional writing style standards can be found in the Chicago Manual of Style, available in any bookstore.)
Plan it out. Don't make it up as you go along, and don't improvise. Decide early what you will write, how you will write it, what points you will make and how many words you will use to make them. Stay on target as you write.
Use active verbs. Write about nouns that verb ("Susan opened the door") - not verbs that were committed by nouns ("the door was opened by Susan"). Passive verb construction is an early sign of overformalized language. Take out the extra words and get that subject back up front.
Use plain language whenever possible and elaborate language when appropriate. Don't use words that you wouldn't use in normal conversation. Keep it simple - don't use five words when you can use three, and don't use a three-syllable word when a one-syllable word will do. When sophisticated language is required to get your point across, however, don't be afraid to use it.
Listen to the rhythm of the language. Develop an ear for how sentences sound in conversation. Listen to effective speeches and notice how the memorable lines are almost musical. As you write, imagine how each sentence would sound out loud and choose your words for their lyrical quality.
Beware the "I". Avoid the first person in business communications unless it describes significant personal change on the part of the narrator; don't use personal pronouns (I, you, we) in passive verb constructions, or in sentences that don't involve change. Unless the narrator is taking personal responsibility for a significant change in the status quo, leave the personal pronouns at home.