There is really no mystery on how to help transit in Miami. It's a pretty dense area. Buses can work to feed passengers to trains. Buses and trains need to improved in quality and comfort for the passenger (suspension, clear windows, route maps, and stop announcements / displays). They need to be maintained, so they are safe. Buses need to all be electric. Buses need to be frequent and predictable. Phone apps and/or displays at stops need to communicate schedules and any changes. Express buses, light rail, and heavy rail lines need to be extended to cover densely populated areas with N/S, E/W routes feeding from less dense to more dense areas with personal larger vehicle parking in the less dense areas and bicycle parking in the more dense area stations.
Put some $$ into marketing, so people know how and why to use transit. Build elevated lines through busy neighborhoods like Calle 8 or Flagler or Coral Way or Biscyane Blvd.
Just start anywhere and keep going with a 25-year plan. Go look at many cities around the world to see how it's done: DC, NYC, London, Paris, etc.