There are several reasons that Atticus is a good father, and some things he could do better. Atticus is a good father because he sets a good example, and he cares about his kids. He could be a better father because he does not follow through on what he says and he puts his kids in dangerous situations.
First of all, Atticus Finch sets a good example for his children. He explains why he has to defend Tom Robinson, even if the decision is unpopular.
Scout, simply by the nature of the work, every lawyer gets at least one case in his lifetime that affects him personally. This one's mine, I guess. (ch 9)
Atticus expects his children to stand up for what they believe in, and he does the same himself. He does not feel that he can tell them one thing and do another.
Atticus also cares about his children. He plays with them and cuddles them. When Scout and Jem show up at the lynch mob, he is genuinely afraid.
I thought he would have a fine surprise, but his face killed my joy. A flash of plain fear was going out of his eyes, but returned when Dill and Jem wriggled into the light. (ch 15)
Atticus worries about his children, so he clearly loves them.
The incident above is one of the reasons Atticus can do better as a father. He puts his children in dangerous situations. This is not the only time his children are in danger. Someone should have been watching them more carefully. When the children go to Scout’s play, Atticus lets them go alone.
Atticus said as tactfully as he could that he just didn't think he could stand a pageant tonight, he was all in. … He thought Jem might escort me if I asked him. (ch 27)
Alexandra does not go either. Atticus does not even insist that Jem goes, he just suggests it.
Finally, Atticus threatens to punish his kids if they disobey him, but he does not do so. Jem says that Atticus has never whipped him.
This was a thought. It seemed that Atticus threatened us every other day. "You mean he's never caught you at anything." (ch 6)
Atticus tells Uncle Jack he has been able to get away with just threatening. Still, if a parent says he will do something, he should follow through. If Atticus’s kids were not good kids, he would have real trouble with them.