I'll cover letters and emails but, before I do, there are some ground rules.
1. Never write in an angry vein.
2. Keep the letter light and humour helps, but not too much humour.
3. Tell them, at the end what action you want them to take.
Point 3 is important in all business letters. Over the years, 99% of all the sales letters I received twittered on about their product and ended with Yours faithfully, never asking me to take any action. Naturally they went straight in the bin. Asking for action would have delayed going into the bin for a brief moment and that is all a salesman can hope for.
A letter of complaint:
First of all, send it as soon as possible by first class.
At the top of your letterhead, write: "Sent by first class post" and underline it.
This indicates that you wish the reader to take immediate action.
Start off with a short paragraph explaining the nature of the complaint.
If you have been a satisfied user of the company's services or products for some time, a brief paragraph explaining this here, saying how happy you've been in the past.
Then a paragraph or three detailing in chronological order everything that has happened concerning your dissatisfaction. Be factual, and as I said above, don't let your anger seep through to the letter.
Penultimate paragraph summarising the complaint in a very short paragraph, a sentence if possible. A busy executive may just copy this to the department head concerned, or highlight it if he is going to copy it to the manager. Better it is in your words.
The last paragraph should tell [not ask or suggest] the CEO exactly what you expect if he wants to keep you as a satisfied client. Adding the word "satisfied" gives you an out to return if you don't get what you want.
If you don't hear from the CEO within a week, send a copy of the letter, with a note saying "I'm a little concerned you never received this, please could you confirm receipt?" This will let him know that you aren't going to go away.
If a complaint detailing a minor item, you can send an email, but it is never as effective as a typed letter.
Keep the the same pattern as the letter, except change the part I call "A paragraph or three" above.
Here, itemise each part of the complaint with points as CEOs get hundreds of emails a day, and can't take in too much unbroken email text.
List your first point here in detail but try to keep it to 140 characters (thanks Twitter).
List your second point here in detail but try to keep it to 140 characters (thanks Twitter).
List your third point here in detail but try to keep it to 140 characters (thanks Twitter).
Incidentally, using Point or Item or Question in the same format is always useful when writing emails to companies, especially when asking questions. Harassed executives usually pick the easiest point or question to answer hoping you'll go away. This way he's forced to answer them all.
I have used this method on many occasions and it normallyAmpers.
has very positive results.