[Poiesis]

Step one is to be aware of your capacity to hurt; it seems like you have this covered. I find that over time my awareness has grown, which has caused me to care more (and be more careful) about the feelings of who I am communicating with.

I used to think something like, "If I can just get them to see that I didn't mean to hurt/mean it that way, they clearly won't be hurt!" This is not at all true for many (most?), and like many matters of emotion that's ok. I was not originally aware of the phrase "intent is not impact" but this idea is what I'm trying to describe above.

It is very important to approach this from a place of humility and non-defensiveness. Be eager to apologize for the hurt you caused. I'm sure you're a great person who doesn't wish to hurt people; apologizing doesn't mean that you're sorry you tried to hurt them but that you're sorry that you did. Think of it as the equivalent of apologizing for accidentally elbowing someone in the head. It's not like you meant to, but their head still hurts where you elbowed it.

Actually caring helps a lot; it helps remind you to think before you speak or write, and to pay attention to reactions. If you care, you tend to get better over time.