Find an ocean or river at night
Kill drowned that are holding tridents
Use a Looting III sword to increase drop chances
Search for drowned in ocean ruins and shipwreck areas
Use a trident with Loyalty or Channeling if you already have one to farm more drowned safely
Check for drowned spawns in water caves and deep ocean biomes
Build a drowned farm to get tridents faster
Use a sword with Sweeping Edge to kill groups of drowned quickly
Increase your render distance to spot drowned more easily
Keep farming until a trident drops