Good parenting is composed of many things, and it is a challenging undertaking. This is especially true since there are no perfect parents. The best parents are the ones who are at least concerned with trying to be as good as they can.
Bad parenting is easier to define. Whenever we parent our children out of a place of emotional injury we are being bad parents. The reason for this is that when we are in a place of emotional injury, we need to be taken care of ourselves. We are, in effect, asking our children to take care of us. This is a reversal of the parent/child relationship, where the parent is available to take care of the child.
When this happens, we are eliciting a split that takes place in the child. There is an aspect of the child that knows that its parents, giants who have the power of life and death over them, that responds by taking care of their parent, so that they can survive. This is done out of fear. Simultaneously, there is another aspect of the child that knows intuitively that this is a reversal of the parent/child relationship, and is angry. This angry aspect feels rebellious. Whichever aspect becomes dominant, they are both likely present to some degree.
Parenting, even more so than life before parenting, is filled with injury. Children are dependent, and dependency is difficult to deal with. They start out completely and overwhelmingly dependent, and gradually gain more independence as they grow. As a result of all of the injuries that parents experience, from sleep deprivation to financial demands to the struggles of adolescence, parents also experience anger. Frequently the injuries intrinsic in parenting are compounded by the parents' own childhoods. Since there are no perfect parents, no one escapes childhood unscathed. It's only a question of how much damage you receive. When your own parents have been especially difficult, its inevitable that you may have some resentment for your own children, especially if you are making their lives better than your own was.
Injuries to parents, and, therefore, anger, are inevitable. The question becomes one of how to protect your children from your difficult feelings, given that you won't be perfect at trying to do this. It certainly helps if you made a conscious decision to have children, and didn't feel trapped into it or stuck with it.
One obvious piece is to try and give them as much positive love and caring as you can. Also, try and say "No!" to them as little as possible. That means it will only seem like you are saying it most of the time. Additionally, you'll need to be paying a lot of attention to your own emotional state when you're around them. If you notice that you're feeling injured, angry, or scared, then you have a chance to intervene and protect them from your own emotional needs.
It's a tremendously challenging yet rewarding experience. Good luck, and remember, when you do mess up and act out your own feelings, it's important to come back later and apologize!