Start with civility.
Put aside hate.
Respect your interlocutor,
despite their political or sociodemographic disparities.
Assume good faith.
Listen carefully to what is said.
Withhold judgement.
Assume you may learn something useful and most likely you will.
Respond to what is said,
not what you imagine is really meant.
No standing up straw men by misrepresenting what was said.
No personal attacks, especially labels of opprobrium.
No changing the subject if things are not going your way.
Argument is better when it's not a contest
but instead a mutual enquiry towards better understanding.
Illumination should be the goal, not victory.
Mostly the ideal outcome of argument
is not convincing the other party (or bystanders),
but mutual identification of specific principled disagreements.
More specific is better.