In daily conversation, use polite words such as please, would, could and thanks, which are meant mostly for service people, not close friends.

In professional situations, replace thanks with the reason why you thank him, for example: “The incredible professionalism you showed in your service is greatly appreciated. This couldn’t have happened without your help”. Similarly, replace sorry with the reason why you apologize. To learn this, just follow some politicians on Twitter, they are professional with this skill.

During intense arguments, replace the bad or rude words with the literal reason why you want to say it, for example, replace “I don’t give a fuck” with “you don’t deserve my attention”, replace “it’s none of your business” with “I can’t see how that matters to you”. Of course before things got intense, you should try a polite way to avoid escalation of the situation, such as “the way you talk is starting to make me uncomfortable”.

General suggestion: Just watch movies and videos, but not those kind of action movies which are full of dirty words. I’m also a non-native speaker but I’m pretty satisfied with my current English skill as a non-native, including the ability to speak politely. I have a European C2 level certificate for English, the highest level for non-native.