1) One of the most common causes for excessive barking is lack of exercise. Make sure you provice your dog daily with both physical and mental exercise.
2) Resolving the main cause of the problem will make your dog much calmer, but this alone wont make the bad habbit of barking go away. Once your dog starts barking, slap your hands to get her attention and say NO with a calm but firm tone. Never yell at your dog, for a dog yelling is barking.
3) Basic training also helps to resolve this problem. You can negatively reinforce this behavior by giving your dog a command that you know is unpleasant for her. For example as soon as she starts barking, tell her to stop as described at step 2 and then order her to lay down. This is also to keep her busy in order to prevent her to start barking again. Dont play games with her to get her attention as this will reinforce the unwanted behavior and make her bark simply to get your attention to play games.
4) Be consistent. Always use the same command to make her stop barking and make sure you insist untill she stops barking.
5) Be calm. You are trying to make your dog calm by giving the example.
6) Teach your dog the talk command. Surprisingly it helps the dog to understand better when you want her to bark and when not to.
7) Read again step No 1 ! Good luck and enjoy a calm confident and not loud dog!