The 90/10 promotion rule: what to do with the 10%?

I said a while ago that I favour the 90/10 rule for self-promotion on social media. In other words, if you spend 90% of your time there being generous - offering my three pillars of Friendship, Information and/or Entertainment - people will allow you to spend the other 10% promoting yourself, whether that means mentioning that you have a book out or telling your friends about a nice review, or