Among the weirdness Facebook's existence has loosed upon the world is the idea that it's OK, and perhaps even good business, for brands to sidle up and give you verbal balm for your case of the Mondays, ask for predictions on the big game and offer random thoughts on things that have not a whit to do with their product or service.

The touchy-feely strategy is meant to be conversational -- human, even. But new data from Facebook itself tell us that what looks good on the social-media guru's presentation deck isn't the best approach for making Facebook work for the brand. 

Facebook recently ran a monthlong study that looked at more than 1,200 posts from 23 brands. After tagging each post for various attributes, the measurement team plugged them into a quantitative model that turned out to be quite effective at predicting which posts will yield more engagement in the form of likes, comments and shares.

"By far, the biggest predictor of engagement was that the post was on a topic relevant to the brand," said Sean Bruich, head of measurement platforms and standards at Facebook. "It impacts everything, from lightweight likes to more invested shares. It's actually one of the most important things a brand can do. People are seeing the content because they liked the brand, and it makes sense that content about the brand will get them engaged."

Despite this evidence, Facebook isn't explicitly telling marketers to ditch their most purely conversational posts. "In general, unrelated posts are not predictive of increased engagement," said Mr. Bruich. "That being said, we're not arguing against those types of posts being a nice change of pace. "

Check out Skittles' page to see a brand that 's made its own rules, cultivating a weird world where normal definitions of relevance don't really apply. For instance, "Like this post if you agree with what I'm going to say tomorrow" fetched more than 10,121 likes, more than 400 comments and just 21 shares. Meanwhile, a picture of a football helmet made of Skittles got more than 400 shares, which is pretty good.

But, of course, not every brand can be Skittles, and the average brand, according to Facebook, will do best to hew closer to the topic at hand. 

Another important finding was that asking people to like a post indeed yielded more likes, but it didn't do much for the other forms of engagement, including the all-important share action that sends a brand's post into a users' timelines for all of their followers to see. Compared with likes, shares represent a bigger investment from the consumer and occur less frequently. Thus, shares are often going to be more meaningful from a marketing perspective. After all, they suggest the brand is tapping into that friend-of -fan network that 's central to Facebook's viral proposition. 

To get more precious shares, Mr. Bruich advises posting more photos and videos. Asking questions of your fans increases commenting, but not liking and sharing.  

These findings hold true across verticals. "There's some order to this universe," said Mr. Bruich. "There are general truths."

The notion that a stable body of knowledge is building up around Facebook should be comforting to the many marketers that are plowing more money and attention into it. And this isn't the only evidence that we're moving past the days of fly-by -night observation about what works.

Buddy Media, the analytics company that works with more than 600 brands and agencies on their social-media presences, is set to reissue a year-old paper on Facebook best practices. The company, according to a spokesman, has found that the report is standing the test of time, with its industry-specific advice on posting schedules and thoughts on using "softer-sell" keywords still relevant. It mainly needs a new introduction.

Buddy Media found that brand fans are more willing to comment when asked a question, especially if the question begins with "where," "when," "would" and "should." But other interrogatory words don't work as well.

"Avoid asking "why' questions," advised the Buddy Media paper. ""Why' has both the lowest like" and comment rates and may be seen as intrusive and/or challenging."