KNOW YOUR PACE. BE REALISTIC
Pro athletes practice executing the distance and metrics they are aiming for on race day including pace, watts and heart rate at, or close to, race distance across all three disciplines. The pace athletes can hold on the bike for longer than four hours will likely feel very easy in the first hour, but by hour four or five will feel very hard. Figure out what that pace is by experiencing it in training. Knowing your pace will also help you gauge how long you will be out there which is necessary for tip No. 2.