My Friend's dog has so many bad behaviour like:
Barking at people unnecessarily, fighting other dogs, bringing dirt in the house, defecating anywhere in the house and lots of others.
My friend usually ties it up and doesn't give it food in order to discipline it. But I've told him that is not the best way to discipline a dog as it might make the dog violent with him.
What is the best way to discipline this dog?
Depriving a dog of food is not a productive way to discipline a dog.
From the sounds of it, this dog needs a lot of attention, in the form of training and fun dog activities.
Useful methods to discipline dogs are ones that will teach the dog. Dog's are intelligent animals, but they have an intelligence similar to the level of young children (<=4 years); so they cannot understand elaborate consequences, they respond to simple cause and effect whether it be positive or negative reinforcement.
The best way to discipline a dog is to proactively train a dog.
From the sounds of it, it would appear that your friend's dog has not been trained much, if at all.
These are all symptoms of a bored dog that has not been well trained or socialized.
Balancing positive and negative reinforcement with dogs is important, as continual negative reinforcement without praise can cause a dog's nature to become less friendly.
Some tips would be to try and train the dog the basics, a reward based training system is good. This PDF by the Australian Veterinary Association gives good advice on how to apply positive rewards for good behavior and appropriate punishments to deter unwanted behavior.
There are two types of reinforcement techniques
Positive reinforcement involves giving the dog something it wants to make the behaviour more likely to occur again. This occurs if asking the dog to sit and stay and giving it a reward (something the dog wants) for staying away from the biscuit on the table increases his likelihood of doing as asked again.
Negative reinforcement involves removing something aversive to make the behaviour more likely to occur again. This occurs if holding the dog back from the table by a tight choker chain (an aversive stimulus), and releasing the pressure when the dog sits down and stops leaning in towards the biscuits. This results in the dog being less likely to try and approach food on the table in the future. Note that an aversive stimulus had to be present (the choker) for the dog to have to work to escape, so negative reinforcement can also be called escape or avoidance learning.
Personally, I like to train dogs with a style of integrating positive or negative reinforcement with my own natural body languages. The voice should always be used when praising or correcting, and the pitch and tone of the voice, that's a good dog and a good pat with a food reward; or a firm and deep No! and a loud clap of the hands with either a spray from a water bottle, or check from a check chain. This causes the dog to associate your voice and actions the external stimulus, so that eventually the external stimulus can be removed.
As Skippy said in his answer, tying up the dog and depriving it of food is simply cruel and doesn't teach him anything (otherwise, he would have probably seen a difference by now).
Dogs (and other animals, including ourselves) learn through operant conditioning. There are other mechanisms but operant conditioning is the one that is involved when you're trying to teach your dog a certain behaviour.
Following are some definitions from a similar answer of mine that should help explain the different terms:
These terms can form four different combinations (N.B.: Examples in brackets are examples, not advice!):
So you have four basic techniques with which you can train your dog to perform or stop performing certain behaviours.
According to science, positive reinforcement outperforms any of the other techniques and is even better than combining any or all of the techniques (see, for example, Blackwell et al., 2008; Hiby et al., 2004).
But regardless of which one is most effective, the real question should be: What relationship do you want to have with your dog?
Positive punishment and negative reinforcement involve making the dog at the very least uncomfortable if not outright hurting him. Neither will make your dog happy, nor will it help to build trust between you and your dog if you're a source of unpleasantness. Furthermore, these techniques only let the dog know what you don't want it to do.
Positive reinforcement, on the other hand, basically ensures that your dog thinks that "only good things come from you". It helps to build trust and love between you and your dog and will make your dog a very happy one.
It's not always obvious how to teach certain behaviours using positive reinforcement (for example, when the objective is to stop a behaviour) but just ask a question about whatever problem you're facing and feel free to ask for positive reinforcement techniques specifically.
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