The most reliable way to get gold, grain, and soldiers in King's Throne: Game of Lust is through levies. Check out our What are Levies guide to find out everything you need to know about them.
When you tap your trusted advisor Marcello in the throne room of your castle you will be taken to your Levies screen where you will be able to collect resources such as gold, grain, and soldiers. Gold is used for upgrades, grain is used to recruit soldiers, and Soldiers help you in the PvE and PvP battles so it is important that you regularly collect these resources. If you run out of attempts, you can use Royale Levy Seal to collect/recruit again. Royal Levy Seals can be obtained from the VIP Rewards, and completing Daily Quests. The number of Levies that stack and can be collected at a time can be increased by progressing to higher kingom level but in order to increase the amount you recieve from each Levy you will need to upgrade your heroes' respective skills. Although you can get a fair amount of resources from Levies it is by completing the various quests that you will get the biggest rewards.
Check out our What are Royal Decrees guide to find out how you can get additional rewards such as EXP, Gold, Grain, Soldiers, and Atrribute Tomes by issuing Royal Decrees.