When making complaints in writing, carefully review your email or letter before sending it. Remove any words that are vulgar or profane. Don't make sweeping accusations: "Your agency is a waste."
Don't attribute motives to people you've had problems with, such as: "The postal clerk refused to help me because he's a drunk." If the person actually appeared to be drunk, then be precise in your description: "As he leaned over the counter I could smell beer on his breath. Behind him, in a waste basket, I saw an empty bottle of Coors beer."
Show how the failure of the official to address your problem reflects badly on the company or agency: "This is not the level of service your ads would lead potential customers to expect."
If necessary, note any regulatory agencies that can make life rough for the company or agency if your complaint isn't resolved. For the phone company, for example, cite the FCC or the PUC. But do this only after you have stated you hope your complaint can be settled amicably and privately within the company.