In Clash Royale, you can earn Gold by:
Firstly, the easiest way to earn Gold in game is opening Wooden Chest, Silver Chest, Golden Chest and Crown Chest. Attempt to open them whenever you can by playing a few battles in game everyday to take all that easy and sweet money.
Donating is the second way to earn Gold in game. Some players think it’s stupid to give the hard-earned cards away. Yes, it’s pretty hard to get them but you can get XP and 5 Gold for every donated common card and 50 Gold for every Rare. The Gold is not taken from the player getting the card from you. It’s just like you are selling cards but the buyers don’t have to pay. You can donate in total 60 cards everyday, that’s 300 Gold everyday and 2100 Gold every week (or even 4200 Gold every week If you usually donate Rares). By donating, you can buy 1-2 Epic Card from the Store everyweek! That’s very crazy If you don’t want to get that free epic because It’s much harder to get those cards than the donated ones.
Also, as long as you keep requesting cards, you can always take your cards back, so why not give them away, right? You can request 3 times everyday and 10 common cards at a time. I usually keep requesting Barbarians and donating them whenever I can because most players use Barbarians.