OK ENOUGH!!! All this advice is wearing me down. Here it is in a nut shell:
1) hand wash only with lambswool. If you cant use lambswool, use terry cloth, but it can leave swirls. The terry cloth's "loops" in the fabric hold dirt out of the way so they do not get ground back into the surface. Machine wash your mitt or terry cloth after every car wash, and DO NOT USE FABRIC SOFTNER-it clogs the loops, preventing contaminate pickup.
2) Use the right soap for the job. Brand new cars need a "gold colored" soap. I prefer Meguiars Gold Class soap. It, like other gold colored soaps, have clear coat conditioners. DO NOT USE DISH SOAP OR DRIVE THRU CAR WAS SOAP!! They are heavy duty surfactants designed for 1 thing-to strip a surface of contaminates, including waxes, polishes, and can dull (haze) clear bras.
3) DO NOT DRY WITH A TOWEL , TERRY CLOTH OR OTHERWISE. If you have cleaned the surface properly, rinse without water pressure, allowing the water to cascade over the surface. You will find drying with a squeege or chamois much faster, easier, and no streaks. This is preferable especially if washing in direct sunlight. Dry from the top down starting witht he roof, the the windows, etc.
I have been detailing professionally for 20 years. There are numerous reputable car washes that wash by hand in every city. ]
I hope this helps you maintain that showroom finish.
Happy washing!!!