Best Strategies for Efficient EV Training in Pokémon?

Hi everyone,

I'm looking for advice on the best methods for efficiently EV (Effort Value) training Pokémon. What are some of the most effective strategies or tips you've found to speed up this process and maximize your Pokémon's stats? Are there specific items, locations, or Pokémon that you find particularly useful for this task?
level devil
Thanks in advance for your help!