I tend to upvote a post when it Links an interesting article or provokes an interesting conversation, and only downvote them when they voice an convectively bad opinion (like, bigotry or other unjustified vitriol).
I tend to upvote comments when they make a good point or at least try to support their argument, and only downvote them for the same reason as posts: when they are trolling, being unnecessarily aggressive, or trying to justify bigotry with fallacious reasoning or something
What about you?
For posts, it comes down to whether or not it fits the community. In /c/UnpopularOpinion, your opinion had better be unpopular. In /c/Funny…well, bad example. 😆