To start a Casino Heist in GTA Online, gather a team of players and ensure everyone has the necessary skills and equipment. First, purchase the Arcade property to unlock the heist planning feature. Complete the setup missions to gather intel and acquire the required tools. Choose your approach—stealth or aggressive—and plan your escape route. Once prepared, initiate the heist from the Arcade's planning board. Communicate effectively with your team during the heist to maximize efficiency and ensure a successful getaway with the loot. Good luck!