Though shalt use two sponges
Never use fabric squares, as they leave fibres behind and in the end your job will look botched. Car wash mitts are recommended, but nothing beats a good ol’ sponge of the right size. Make sure you use a dedicated sponge for the rocker panels, and a second one for the other parts of the car. This way, you won’t spread dirt around when you realize you’ve missed a spot and have to start over again.