The first step to stopping barking is to understand why it is happening. Dogs bark for all kinds of reasons, including anxiety, boredom and/or loneliness. Sometimes they bark just because it feels good.
Luckily, most dogs will respond to one or other intervention to curtail their barking. Whether you simply bring an outdoor dog inside or take the time to apply behavior-modification techniques, you can cause a dog to be less of a nuisance and to be more socially acceptable.
For more information, please read the story When Barking is a Problem.