It's inevitable; at some point in your life (probably at many points), you're going to get a faulty product or bad customer service and you'll want to complain to someone who can do something about it. How you complain is often the most important factor in getting a resolution.

1. Complain as soon as possible after you discover the problem.
2. Gather all of the necessary paperwork -- receipts, cancelled checks, invoices, bank statements, rental agreements, etc.
3. If possible, complain in person. If that's not possible, use the phone or email.
4. Be concise. Rehearse what you're going to say, so that you can get to the point quickly.
5. Be polite and friendly. The person hearing your complaint probably isn't the person responsible for the problem, and you'll get nowhere by being rude.
6. If the employee hearing your complaint can't or won't help you, ask to speak to a supervisor. If the supervisor still doesn't help, keep going up the chain of command.
7. Keep a record of the names of people you speak with -- including the date and time, and what action was promised. If you complain by email, keep every exchange.
8. Ask for a deadline. "I can expect to receive that refund check when?" "I'd like to have those repairs finished by Friday; is that possible?" Make a note of what is promised.
9. Be flexible. If they can't meet your request exactly (i.e., they won't give you a full refund), ask what they CAN do (will they offer you a gift card or store credit for the same amount?).

Here's a link to a website with a "general complaint letter" template. It can also help you prepare your thoughts if you complain in person or over the phone rather than in writing.

HowToComplain.com