There are some objective factors like spelling, time spent creating the content, quality of the pictures/text/video, knowledge and expertise on the topic etc and other subjective stuff like opinion of the curator, preferences, expertise on the topic by the curator (for example I can't asses if a painting is good, but we have curators that do) and some others.
The good thing is that we have many curators focusing in finding great content for over two years now so we hope to deliver on the community's expectations.
You can add "verifiable sources" to back the statements made in a post, especially if it contains any scientific topic.
Also if there are lots of comments and real discussions in a post, that's an indicator of interesting content.