What is the quickest way to raise Affection?

It's similar to raising affection in the 3DS games - play with them until their play meter is maxed out, then feed them, then go back to playing. It's a little more efficient now as you can raise two at the same time. This is the method that works best for me:

  1. Set up a Pokémon Camp
  2. Face the two Pokémon you want to raise and Call them over to you
  3. Get out the feather/bell like cat toy and wave it around (I just mash the A button) in between the two. The two Pokémon will attack it over and over, each time letting off some orange notes
  4. After a while, the Pokémon will stop attacking, stand still in place, and release a speech bubble with orange notes in three times in a row - they are now ready to move to the next step
  5. Cook a curry - I don't think the quality matters too much, but it doesn't hurt to aim for a nice one. Wobbuffet or higher should be fine, though
  6. Go back to step 2 and repeat
  7. At various points throughout this procedure you will see pink hearts instead of orange notes - this indicates they've gone up an affection level. Once they reach the maximum level, instead of orange notes at step 3, you will get nothing at all - this indicates the affection is maxed out

It's useful to max out the affection as soon as you get anything you're planning on keeping in your party. Especially a Farfetch'd/Sirfetch'd - with maxed affection and holding a Leek, every single attack it makes will be a critical hit!