I’d get people from Nextcloud onto podcasts with decent size audiences. TWiT has proved effective for some other projects I’ve advised. Returning to the Linux Action Show. Anything on iTunes catering to tech startups, SMB’s etc. Podcasts are always looking for people happy to be interviewed who can offer their listeners something valuable at no cost.
Give and promote Nextcloud talks at conferences and record instructional videos about Nextcloud. Live demos and testimony are very convincing for would-be users and admins.
Example talk with details helpful for self-hosting:
Example conference that has had Nextcloud talks in the past:
Pardon the self-promotion here… I was not paid for any of this.