You can't tell people how/when to upvote/downvote/do nothing. It will not work and people will try to game the system. People will vote based on instinct.

For example I upvote what I like/agree with. I downvote stupid or wrong stuff.

That being said, I think the HN community has regulated itself remarkably well so that truth/content gets sufficient votes and falsehood/noise gets downvoted, and heavily so if needed.