There are scads of articles for how to maximize "engagement" on the net, however, for the purposes of authors, most of these recommendations are completely misguided.
Before I get into why these internet pundits are wrong, let me clarify what that term "engagement" actually means for writers.
Engagement, as a marketing term, means getting someone to buy something or exhibit interest in your product in some tangible way. If you are a writer, engagement means getting someone to buy your book, or write a review. If you are a blogger, it means traffic to your blog. If you have launched an author website or Facebook page, it means having people visit, read your page(s), and make return visits.
In short, engagement boils down to numbers.
Keeping that definition in mind, how does it benefit you, as an author, to enter into an online fracas with a person whose sole purpose in life is to annoy people? In fact, some of these "trolls" are even willing to pay for the pleasure of harassing writers. (Read Derek Haines' story here.) Now, if you were riding on a bus and a complete stranger sat down and starting berating you, you would simply get off the bus. It would be useless to try to argue with them. When someone does that online, it is equally as pointless.
If you are a budding author here are a few simple rules to follow when embarking on "engagement:"
1) If someone makes an insulting comment on a public forum about your book, or anything else you've written, do not reply, even to defend yourself.
2) If someone writes a spiteful comment on your blog or Facebook page, delete it.
3) If someone writes an inappropriate review, personally attacks you, or uses your book for a negative ad campaign, make a complaint. Do not address the "reviewer" directly. (Some of these "reviewers" get paid for driving down the ranking of competing titles by posting negative reviews. Recently, on Amazon, I found 22 identical negative reviews for books on pain management, all of which were posted within a two-day period. I flagged every one of those reviews as inappropriate.)
4) DO NOT post your opinions on blogs other than your own, or any other public site.
5) DO express your thoughts in interviews. Interviews do more to help build your profile than leaving a comment on a blog, and interviews have the added benefit of providing a buffer. (Suggestion: Book reviewers frequently post author interviews.)
6) DO reply graciously to people who give your books a thoughtful review, or who leave good comments, but only if the site is moderated, or if it is your own blog, website, or Facebook page.
Reward people who behave themselves. Ignore those who don't.