Civility begins with assuming good motives
A few years ago, when I objected to President Barack Obama ordering the assassination of an American citizen named Anwar al-Awlaki via a drone strike, a Leftist troll accused me of being a white supremacist who was siding with Islamic terrorists because the President was a black man. It was an absurd attack that was meant to avoid any serious discussion of civil rights, due process and the limits of government power by smearing me with the fraudulent allegation of "racism."
So here is a thesis: We should generally assume that the people we argue with and against want the best for our country. They want our country to have liberty and economic security. We may violently disagree with their policies, and we may think that those policies will be ineffective at best and destructive at worst, but we should assume we have patriotism on both sides and a belief in the idea of America.
This is not a call to be naïve or to not practice discernment. We should not do that. There are legitimately bad actors in politics at the local, state and national level. Those people should be called out, and a general civility does not preclude us from calling out such people.
But generally, people want what is best for our nation. For example, I believe that abortion is a moral abomination, but those who favor abortion rights do not take glee in the death of unborn babies. They are worried about government intrusion in people's lives. Those who support "card check" support a bad policy that I believe is harmful, but they want unions to be strong to advocate for employee rights. Those who support government spending I find wasteful do not want to spend our nation into bankruptcy. They want to help people with programs they find useful. Those who support a liberalized immigration policy do not want MS-13 terrorizing our neighborhoods. They want to offer the promise of America to more people.
I could go on with many more examples, but you get my point. I can disagree with open borders advocates, union representatives, abortion rights supporters and even socialists without thinking they are all evil people who are trying to destroy our nation. Meanwhile, those who disagree with me on policy can think I am wrong without thinking I hate immigrants, I want to oppress and enslave women, or that I am a greedy person who does not want to help those in need.
Furthermore, it should be obvious that we can disagree with various uncivil actions (such as harassing people at home or in public) and call for more civil behavior without getting into a childish game of whataboutism. "He did it tooooooooooooooooooooo!!" is not an argument, it is an attempt to avoid accountability. At the same time, we should call out uncivil behavior on our own side.
Most importantly, we should model civility in our own behavior and rhetoric. I have often failed in this regard, too willing to directly attack the person when I should instead make an ideological argument. Again, this is not to say that no attacks are justified or that there are not legitimately bad people. Obviously there are bad people. But I need to do better, especially in modeling behavior to my sons.