Add Glide apps you’ve created to your profile—make sure we can review them (they must be public)
Become active on this forum to get added as a Community Expert
Collect three endorsements from people you’ve helped build apps and email them (together, as one email) to hello@glideapps.com with the subject “Glide Certified Expert Application” to apply for certification.
The links and comments above make it pretty clear. I’d say read through the Glide docs and watch the videos. Read and participate in the forum. That’s were you learn what you can and cannot do along with all the tips and tricks from others in the forum. Develop some apps to show off your skills. I don’t know how often Glide reviews and excepts users as glide experts, but I’d guess it’s not hard set rules. More or less just prove that you know the ins and outs of everything.