A Whiteout Survival farm account is probably the most efficient way to get resources consistently in this game. This is basically an extra account that you can use to gather resources, and then transfer a large number of them to your main account. This strategy will help you prevent overloading your Infirmary with low-tier troops. This is important because if your Infirmary becomes filled with low-tier troops, it might result in your higher-tier troops not getting the medical attention they need...