One of the best ways to earn them is by playing Desert Island Escape or Puzzle League. Each time you beat the target score in a round of Desert Island Escape, you earn two MEOW coupons. For Puzzle League, you can get one MEOW coupon for each of the following:
- Completing a story round in a short period of time
- Getting 5 chains (once a day)
- Getting a 10-combo (once a day)
- Getting 10,000 points in Score Attack
- Getting 2,500 points in Time Attack
- Getting 10,000 points in Garbage Attack
- Clearing 100 candies in Candy Mode
Unless you scan Wisp/the Villager. I've been doing that for a couple of days, so I can purchase the items from his RV, and he doesn't give the extra 5 coupons for that.
For someone like me who doesn't play with amiibo cards, I usually grind MEOW coupons by playing Time Attack mode on Puzzle League. You gotta hit 2500 every time which can get a little stressful because there's a 2 min time limit. If you practice a bit it's quite easy to get the hang of. You can farm them because there's no limit to how many a day you can earn. If you have amiibo cards though I suggest just scanning them in every day.
I'm gonna be honest though, amiibo cards are nice to have. I got into collecting them so I could bring my villagers back if they moved without telling me.