I use the Maquires NTX tech wax and car wash soap.(Good Stuff)
As stated before wash in the shade using a microfiber cloth.
Shamis with a real shamis to get most water off then redry with another quality microfiber cloth...I use this same damp cloth, to wipe the door jambs, inner doors and trunk when done
Finally very lighty dampen another clean microfiber cloth and rewipe the whole car again...it will GLOW after this step.
It sounds like alot..But I can do the full wash in under an hour..Waxing it too takes a bit longer.
DO NOT rub your black car in small circles like the karate kid with wax or wash this will cause swirl marks over time..always wipe with the "grain" as it were..lol
This system will prevent water spots no matter how hard your water...As for spots from rain water or irrigation sprinklers..I can only recommend and good coat of wax and a garage.
And yes..I do own a couple dozen Micro cloths...