Hire directors/writers who are either fans of the source material or willing to do their research to understand the essential characteristics of the characters in their films.
They need to favor a collection of movies that just happen to be in continuity with one another instead of a “cinematic universe.” Man of Steel, unlike Green Lantern, was really not designed to be a mainstream popcorn movie that could support an expansive franchise. Batman v Superman seemed downright impatient with itself whenever it had to engage in studio-mandated world-building when it was really wanting to tell a more intimate story. Maybe the path to Justice League wouldn’t have been so rocky if BvS had ended with Batman rescuing Martha Kent, saving all of the metahuman cameos and the death of Superman for a less moody, more typical summer blockbuster-style sequel. But what’s done is done.
Frankly, there’s little need to reference the events of Man of Steel, Batman v Superman, or Justice League going forward, at least not directly. Superman gained some perspective after dying and now has a less dour attitude. Batman is over the existential crisis that led him to go on a killing spree. All of the heroes are superfriends now. There’s your de facto reboot. Give us Henry Cavill taking on Mxyzptlk, with a cameo by Shazam. Give us Cyborg and Flash teaming up against the Weather Wizard. Build some good will and then have the band come back together to take on the Legion of Doom, swamp HQ and all. But don’t treat it like a big deal. It’s not the culmination of some grand story arc. It’s not an Earth-shattering crisis. It’s just another exciting episode of Justice League. That’s all.
To “start” making better movies?! Wonder Woman, Aquaman and Shazam have all been solid films. Personally, the best move they did was removing control and director responsibilities from Snyder. Except for Suicide Squad, the non-Snyder films have been DCs best offerings. All fun and entertaining films. I like the idea of focusing on solo films for a while. But I hope they acknowledge the universe out there. Kinda how Shazam did.