Write something worth sending to a specific friend
Since a private share carries unusual weight in the ranking, a caption worth writing is one that gives someone a reason to think of a specific person and send it their way: a useful tip, a funny observation, a strong recommendation. A generic caption rarely earns that reaction.
End with a real question, not a generic prompt
A specific question tied to the actual content invites a genuine reply. A bolted-on "thoughts?" does not. The more specific the question, the more likely someone can answer it from their own experience rather than scrolling past.
Keep it conversational, not written like an ad
A caption that reads like something a person would say earns more genuine engagement than one written in a formal, promotional tone, even for a straightforward business update. The information can stay the same. The voice is what changes.