Sounds pretty obvious, but in most standard businesses 80% of their revenue comes from 20% of their customers, meaning they are an essential priority and they need to be treated as such! Offer interactive customer support aiming for first contact resolution. Delight your top 20% with written thank you cards, offer a free upgrade, know their birthdays and give them special offers, send a gift, discount or anything of this sort! Follow up with people that used to belong to your top 20% in the past with a promotion to incentivize their comeback. This is a great guide to keep customers happy.