How to Sustain and retain the users post launch

Been working on a solid product n the launch of the product, but what's that we need to do to have a sustained spike and retain users who come in to explore the platform and convert them into power users.
Been thinking about this and working closely with teams who have launched in the past and gone through the same problems, Happy to have this thread open to record my findings/ strategies. If there are specific questions, do post, happy to chat!