Re: Things Starfleet needs to fix already on its ships.
The holodecks, serioulsy the amount of times those safeties fail.
As others have mentioned stop making consoles out of explodium. (or employ a 20th century bit of tech known as fuses/circuit breakers and another 20th century bit of tech Seat Belts.
On the continent of wild endeavour in the mountains of solace and solitude there stood the citadel of the time lords, the oldest and most mighty race in the universe looking down on the galaxies below sworn never to interfere only to watch.