What to Write for Effective Complaints

Keeping a professional tone is important, because it conveys the message that you're serious and deserve immediate attention! While it is perfectly okay to speak in the first person, and even use humor (when appropriate), its probably best to refrain from personal attacks and libelous claims against the person or entity you're writing. A good rule of thumb would be to write in a firm, but friendly tone and don't say anything you wouldn't say in front of your mom!
When it comes to a great opening, think of the kind of first sentence that pulls you into a paragraph. Of course, you want it to be relevant to your complaint, but you also want to get the reader's attention. For instance, if writing to GEICO (the insurance company), you could begin with "I didn't save tons of money by going with GEICO". A GEICO executive is now primed for more reading, and they know that you're aware of their brand and campaigns from their commercials that claim you'll save a lot of money.
Though you may be tempted to go on and on giving the minute details of your issue, it is best within the first letter to give enough of the basics, and include your contact information, that way they can get in touch with you if they need more information.
For more help on What To Write, see our Sample Letters of Effective Complaints.