Keeping the first rule of thumb in mind, keep the letter brief and factual. One page should be your maximum. Sometimes, you will find you need more than a page, but those cases are rare. You do not want to lose your reader's attention.
These guidelines are common sense. Sometimes, the writer will get carried away with emotion and forget these rules. Going back and revising will help keep the writer in perspective and the reader on track. It all comes down to effective communication.
Also, be polite, using proper business etiquette whenever possible. Keeping things simple and controlled is the best option, even in letters expressing a dispute or difficulty. The writer is usually looking for a solution, not a war. Without this thinking, you might end up with no solution and cause for writing a new letter--namely, a letter of apology!
Brief and factual is the best way.
One typewritten page or less is the norm for a business letter. This breaks down to approximately 350 to 450 words--enough to get to the point without much fluff.
Business letters in either personal or professional form need to be short, straightforward, and touch on all the facts that need to be presented.
If your initial letter does not fit this criterion, try to shave off anything irrelevant.
What does the letter recipient need to know?
In your letter writing, keep your audience in mind. Is the information you are presenting pertinent to the reader? Is each word something that puts your point across concisely and factually? What will they be expecting as they begin to read? Keep these things in mind upon writing, and then, after the letter is written, read it as if you were the person the letter is intended for. This will help you stay on task.
Keep your writing simple and relevant.
The words you choose say a lot to the reader. Use appropriate vocabulary to convey your thoughts and ideas. If there is a specific "lingo" that goes with the job, use it accordingly and only if you and the reader will communicate more effectively with it.
Go back over and rewrite where needed.
Your first letter should be considered a draft. Once it is finished, use it to correct any incorrect grammar or confusing sentences. Again, remember who is reading this. Please read it as though you were that person.
Is the letter too harsh? Is it too soft for the issue at hand? Is it complete, giving the reader assurance of what you intended to convey? Does it cover every point?
Recruit help and read it aloud to someone.
This helps you "hear" the letter and will also afford you a second opinion, especially if the subject is something you feel strongly about. The person who listens to the letter can tell you how the tone comes across. Remember, as the writer, it is sometimes difficult to be objective.
Check and recheck the letter
You have worked hard on this letter; its message is essential. It is a direct representation of you or whatever party it comes from. Therefore, the tone is fundamental.
Also, most computers have a spell check. Without a doubt, use it! Letters written to superiors or peers send a terrible message if the spelling and grammar are incorrect. This will most definitely sway the reader into believing either the writer could not be bothered to check himself or that they are unprofessional, possibly uneducated.
Consider using letterhead and quality paper.
There are templates to help you select the style of letterhead you want, and the finished product will look more professional. However, if the letter continues to a second page, do not use letterhead for that page. Use plain paper. That said, the types of paper you use will tell something about you.
If your letter is going to a business head about a job, consider a higher quality paper for the letter.
If it is going from you to a friend or relative, possibly a thank you or a person-to-person letter, the quality of the paper will be much less critical.