Never be violent
Let's start with the obvious one, which is inflicting pain, or using physical violence. Dogs, like humans, will make mistakes, and don't deserve to suffer pain as a consequence.
Even if you don't actually hit your dog, but alpha roll, or pin him down, you are teaching him bad habits which he may try to replicate with other dogs and/or even children, thus getting him into even more trouble. Some people are physical with their dogs and then wonder why they are aggressive.
Or say your dog has an accident in the house. Your first instinct is to rub his nose in it. Unfortunately, the only thing your dog will learn from that is to fear you. You don't want your dog to fear you - you want him to respect you.
A dog learns nothing from being struck, and all that you are achieving is a
venting of YOUR frustration and anger.
The other two things you shouldn't do are far less obvious, but nonetheless
essential if you want to end up with an obedient, sweet-natured dog that
understands you. The techniques can be difficult because they tend to fly in
the face of human nature.
Use His Name Appropriately
If you are a parent, you may be used to correcting one or other of the kids by yelling at them - "Jimmy, stop that right now!" In the case of the child, Jimmy knows you are angry with him, as he has been identified by his name; however, with a dog, using their name has the opposite effect, as it actually adrenalizes the dog. So when Rover's owner yells, "Rover, shut up!" - Rover keeps on barking . . . longer and louder. Ironically, he is doing so in a misguided effort to try and please his owner!
Use Eye Contact Appropriately
The final technique governs the use of eye contact. If you study packs of wild
dogs, you will see repeated instances of when eye contact is either withdrawn
or avoided. Again, the rule here is the antithesis of human behavior.
Just imagine your 14-year old son "borrowed" your car one day, and drove all the way to Miami and back, thus committing a dangerous felony, possibly resulting in (at best) prosecution, and possibly a life-threatening accident. When making your point to the teenager that this must never, ever, happen again, and explaining the consequences of his misbehavior, the natural tendency would be for you to be making full-on eye contact just to emphasize how deadly serious you were about the whole episode.
However, if your dog misbehaves, you will simply undermine your correction by maintaining eye contact. Your dog doesn't understand English, so he interprets your lecture as simply "Okay, I guess I've done something wrong, but I know you love me anyway!" Therefore, if your dog is misbehaving, you should immediately withdraw eye contact after verbally correcting him, and that way he will really understand your displeasure.
Finally, a word or two of advice about praising your dog, and most dogs love this from an owner to whom they are bonded. Here, by all means, DO involve both their name and eye-contact, and if you have lowered your body posture to deliver this praise, then he is absolutely sure he is being congratulated, rather than corrected. Praise delivered in this fashion is far more appreciated by Rover than any treat on the planet.