People share stuff online either because they want to appear a certain way (funny, clever, well-informed, helpful) or because they want the person receiving it to feel a certain way (good or bad).
So if you want people to share your message, how could it help with this “virtue signalling” and “emotional gifting”?
You need: 30 – 40 minutes, paper and pen. Write out your core message then try lots of different ways it could prompt people to share. Choose the strongest and concentrate on this. Or test several different versions and see which one goes most viral.