While this may seem obvious, if you look at the majority of social media accounts, most don’t follow the 80/20 rule. The most successful ones do. In order to engage your audience, you need to create content that is relevant to them and promotes engagement.
Purely self-promotional brands on social media will often receive backlash. Let’s take AT&T for example. They used 9/11 as a way to promote their brand. The image of the Twin Towers on its screen with the text “Never Forget” was AT MINIMUM inappropriate (not to mention distasteful, among other things). There are times for self promotion, and this is not one of them.