I always downvote on harsh tone or meanness directed at others (but not directed at myself). I upvote for valuable and interesting information, and intelligently argued points. I try not to upvote for mere agreement (although sometimes it's hard not to), and I never downvote for disagreement. (There are some exceptions - questions that are phrased as surveys etc). Since my time here on HN, it seems to me that most people follow something like this, much more so than on most of reddit where upvote-if-funny/upvote-to-agree/downvote-to-disagree is the law of the land.