It is natural for dogs to bark but excessive barking is unnatural.
Dogs bark for a variety of reasons and understanding the reasons behind barking will help you overcome the problem of excessive barking.
Barking is communication for the dog. Its vocal bark expresses its reaction at anything. It is the dog's way of letting you know about something. Dogs instinctively bark at anything unusual. It responds to the stimulus by barking. Excessive barking occurs when it disobeys your command to be quiet. Distract your dog from barking by a loud clap of your hands. Say the command " quiet " in a strict voice. When your dog responds positively, reward it with praise.
Another reason why your dog barks excessively is that you may have confined your dog to an enclosure for a long time. It becomes frustrated and barks angrily for attention. Exercise your dog by releasing it to run around your garden or walk it around your block on a leash. This curbs its frustration and thus stops its excessive barking.
A dog may bark out of fear or aggression. Your dog may want to be a leader and thus bark loudly to show its dominance. Give your pet obedience training by getting it to please you because you're the leader. Every dog's natural instinct is to please its master and you can reinforce this by rewarding your dog with praise and snacks.
Avoid physical abuse of your dog as this makes it defensive and aggressive. Every animal has the instinct to survive and the dog may become aggressive on you as it follows its survival instinct and defends itself.
Your dog may bark excessively out of fear of you, other humans or animals. This is due to the lack of socialization from young. You have to familiarize it with people and other animals. Teach that the command to be friendly is " hello " and do the same positive reinforcement exercises to encourage it to socialize. If your dog is fearful, don't show your dominance by patting it on its head. Pat it on its chest or neck as these are acceptable areas in " dog language ".
Repeat the positive reinforcement training every time your dog meets a new friend. Gradually, it will come to expect socialization too from the other person / animal and it won't react aggressively with excess barking or other negative behavior.
You may be surprised to know that dogs too experience separation anxiety. You may notice that whenever your dog is left alone, it may bark because it is upset. You can train your dog to expect you to return and hence eliminate the fear of separation. Start with short intervals of separation and slowly increase the timing. Always use positive reinforcements to reward its good behavior.
If, despite your repeated attempts at training and your dog still can't overcome its excessive barking, you can consider other alternatives like boarding your dog at an animal day care center. Please refrain from buying another dog to give your first dog companionship. You may end up with two barking dogs!