Mostly you can get cards through opening chests. You can buy the chest in the shop of the game simply by using your existing coins. However, you can also get chests from events or raids. It depends on the village level on what cards you are able to get. The higher your village level the rarer the cards you will possibly get.
Another great way to collect cards is by trading with friends. Normal Cards can be traded at any time with a limit of 5 per day, and Gold Cards can be traded during special events.
If you don’t want to rely on luck you can simply trade cards with your friends! Normal cards can be traded any time you want, but there is a limit of 5 cards per day. Gold cards are only tradeable during special events.
It is highly recommend to complete card collections in order to get rewards such as free spins and coins.