This sermon actually on two distinct but related topics: your comments responding to the posts of others, and comments others make in response to your own posts. Writing a post is only one part of engaging with others on Steemit, and comments are where the real relationships are forged.
When commenting on posts others have written, make a substantive comment about the post on which you comment. If you agree with their thesis, say why. If you disagree, explain your perspective on the point of contention. if you like the art, explain what appeals to you. If you learned something, tell them what you learned. Do not just say, "nice post," or "I agree." Even if that is all you really want to tell someone, there are too many people on this platform using bots or just lazy copy/paste methods to spam meaningless compliments, and your good intentions disappear into the background noise.
When someone makes a substantive comment on a post you have made, consider replying in kind. A comment thread conversation can help you meet new people to follow. The most fun part of Steemit is finding a selection of other users who post their own quality original content, and following along as they tell their stories.
Steemit is already far too big to find all of the introductory posts by interesting people, so interaction in the comments is one of the best ways to find the ones who are here for the community, and not just the cryptocurrency.