As I said before, I think it would be good if you get in the habit of trying to predict the votes that your posts get beforehand and then not post when you think that a post would produce negative karma.

This is the best advice. The trick to keeping high karma is to cultivate your discernment. Each time you write a post, assess its value, and then delete it if you don't anticipate people appreciating it. View that deletion as a victory equal to the victory of posting a high-karma comment.