The best way (and a must if you want to play competitively) is plunder. Always try to get full plunder every day even by using clone

If you do everything correctly you should get at least 6000 coupons every month for free, 9000 if you're a small spender and even more if you are a GL. That is 1 super rare every 2 months and a little extra coupon for power.

Group wheel gives ~30 everyday on average :v :v :v