This is more of a discussion than anything, but I'm seeing a bit of this lately:
Downvotes without reason. It's your right to downvote, but remember, only downvote if the answer is bad, doesn't answer the question, and so on. And it's very helpful to leave a message when doing so, explaining the downvote.
This is a social website, and people can't improve their questions/answers if they don't know why you didn't approve of their answer!
Close votes without reason. Yes we get a few bad questions every week, some are atrocious, some are off topic, some are too broad, and so on. Some are new people. Help them!
If you're voting to close, welcome them to the site, and explain why you've voted for their question to be closed. It's very discouraging for a new user to come on here, ask a question, and just get it closed off with no feedback. Always leave a comment if you think it'll help.
You can also flag it if it's just spam and needs to go now, so we can have it brought to our attention. Similarly, with other (non-new users), they're here to stay, so help them if you feel their question is bad, off topic or similar - leave a little comment explaining why you're voting to close it.
This is a social site, let's be nice, friendly, and helpful to one another. Plus it's a New Year, a great time to start good new habits!