Aside from voting, there is another important part of curation worth consideration: resteeming. Sharing a post that piques your interest can help spread good content to new audiences. There are also reward incentives that can kick in when people upvote content you shared.
I would caution against excessive sharing, though, because if your original content is drowned in a flood of shared content, people may see no benefit to following you. This isn't some kind of rule, but my personal advice is to resteem no more than you post yourself.
When upvoting, downvoting, or resteeming, I suggest adding a comment sometimes. Make it substantive and relevant, especially when you resteem, try to connect to the material in the post and explain why you found it valuable. "Nice post" says nothing on its own, but remember that even an eloquent comment rings hollow if you don't also upvote.
When disagreeing with a post, remember to keep your comment civil. "You're a jerk" isn't helpful, and neither is, "you're a Nazi." Articulate your objection to the argument, present a counterpoint, and cite your evidence or reasoning as appropriate to the occasion. It isn't necessary to upvote or downvote due to such disagreements. Constructive criticism and debate have a place here, too.
Engagement with authors helps us build a community. STEEM is the blockchain, and there are several platforms to access the blockchain, but community is what connects everything and makes it all work. Comments, curation, and resteeming quality content can all help connect us despite our disagreements and diverse interests.