The Wash
Soak your wash mitt in the soap/water bucket solution and start at the top of the car and work yourself down - roof, front and back windows, side windows, front hood, trunk, the sides, front and rear, and then wheels, tires, and wheel wells. The reason for starting at the top is two-fold.
First, the bottom of the car is the dirtiest and you want to minimize the possibility of dirty contaminating your wash mitt from the start. Second, if you started at the bottom first, then you would simply be rinsing dirty from the top of the car onto your newly cleaned lower surfaces.
It is also a good idea to use a separate, dedicated wheel brush to clean wheels and tires. After you wash each major section of the car, you should rinse the soap off to prevent the possibility of the soap drying on the car and also rinse and hang your wash mitt.
NOTE: It is very important that you use a different wash mitt for your tires. You do not want to use the same wash mitt on your next wash to wash your car's surface after that wash mitt was previously used to clean your dirtry tires full of oils/grime and other harmful contaminants!