This method allows you to fall from any height and not take fall damage. If the floor below is a kill floor, it also allows you to run along that without dying.

Before you fall off the higher ledge, hold space to activate Power Jump, then press shift to start sliding. Doing this means that you won't actually slide, nor use the power jump ability once you reach the ledge. Instead, you will fall off the ledge just like normal, and land on the floor below. You won't take any fall damage, and you won't be killed if it is a kill floor. Keep shift held, and power jump active until you hit the floor.