Generally if someone makes a solid argument or valid points, regardless of whether or not I agree with them then I upvote them. If I disagree I try to reply and explain my perspective.
I reserve downvotes for absurd or baseless remarks, attacks, and other noise.
People like to downvote off topic or sarcastic remarks, I generally ignore them (neither upvote/downvote) because I think making light of topics isn't necessarily a bad thing and can engage people in a discussion.
* I say generally because no one is perfect and I don't strictly adhere to the above.
That's pretty much exactly how I operate as well. I think it would be a good thing if HN tried to encourage this behaviour, perhaps by reinforcing the initial guidelines on signup with things like reminders when down-voting controversial comments.
I reserve downvotes for absurd or baseless remarks, attacks, and other noise.
People like to downvote off topic or sarcastic remarks, I generally ignore them (neither upvote/downvote) because I think making light of topics isn't necessarily a bad thing and can engage people in a discussion.
* I say generally because no one is perfect and I don't strictly adhere to the above.