Inconsistent or Inappropriate Tone
Tone can be tricky. It lets readers know the type of writing at hand — straight-forward, humorous, angry, or scary. But not only must every word support the chosen tone, the tone itself must remain consistent in order to pull off the desired effect.
You can think of tone in writing in the same way you think of it in speech. For example, if you're telling a friend about the rude way someone treated you, every word you use and the way you string your words together is going to relay your unhappiness over the encounter. Plus, your entire diatribe is going to pour out in the same way — you're upset, and you stay upset for the length of your rant. If you start out emotionally, spitting out your words, and then continue by speaking calmly and softly, the impact of your words will be lost and your friend will be very confused.
It's the same way with writing. You choose a tone, and then you stick with it to make your intent clear. But sometimes tone can slip away from you, and what started out as a serious account is suddenly mocking or accusatory. If you're happy with the wording, you can miss the fact that the tone has changed and no longer suits the story. For example, it's not a good idea for a marketing piece, no matter how clever, to make fun of a product instead of touting it.
Read a press release or a letter to the editor. What is the overall tone? Once you determine it, read the piece again and pick out the specific words that put the tone across. Are they consistent?
You can check for tone consistency by checking your wording. Keep in mind the tone you intend as you review and revise. In fact, it's helpful to write down the intended tone and refer to it as you work. If your tone is meant to be funny, check to see that the words you used are light and sarcastic, not academic or cruel. Or if your intent is to persuade people to take up a cause, make sure your language is coaxing and encouraging throughout, not threatening or abusive. Precise wording is key to keeping tone consistent and reflecting the mood and emotional level you have in mind. It's also the way to convey your message to readers.
Inappropriate Language
Once you know the tone of your piece, keep it consistent by editing out unsuitable wording. Inappropriate language comes in several varieties.
If you're writing a book for young children, you need to use words that are appropriate to their understanding and their age. Stretching their vocabulary is great, but you don't want them to struggle so much that they give up in despair.
If you're writing for a general audience but covering an esoteric subject, you need to make sure that the language you use has meaning for the reader, or else provide definitions for any jargon you include.
You probably won't want to include slang if you're writing for an academic audience, while for a hip-hop crowd you'll write more casually.
Whatever age or audience you're writing for, don't talk down to your readers or insult their intelligence. Always assume you're writing for bright, with-it readers — they're reading your material, after all!
For all forms of writing, beware of alienating your audience by using sexist, ageist, racist, or culturally offensive words. When you check your work for appropriateness, though, you don't need to call in the politically correctness police. Just use your common sense.
Sometimes words that have a perfectly innocent meaning in English have a not-so-innocent, or a downright offensive, meaning in another language. If you're writing a speech or preparing copy for other than native English speakers, check with experts for culturally inappropriate expressions.

