I was wondering how users tend to judge what to upvote, what do downvote, and what not to vote on.

I made this comment which got me wondering what others think and do

Personally I upvote almost everything. I see upvote as "this is a good Lemmy post/comment" and downvote as "this is a bad Lemmy post/comment". Most of what I see is good. Bad things are things such as misinformation, bad faith stuff / trolling, people being mean/annoying, bad (in my opinion) takes, people being wrong/stupid about stuff, irrelevant things, etc. When I do not vote it's for one of 3 reasons: either I don't understand what it is saying, it makes a reference I don't get, or I can't determine whether it's good or bad (usually because it's unclear).