I drive my 230SL 3-4 times weekly, so she gets a weekly wash.
My tips as follows, and since I have a black car, I'm extra cautious
1. I use only microfibre sponges
2. gentle, foamy shampoo (ie Ph neutral)
3. I use two buckets. One has the shampoo, other is for rinsing/cleaning the sponge
4. Rinse/clean sponge frequently during wash to not allow trapped dirt to create swirls on paintwork
5. I dry first with a blower. Special attention to rubbers, external moulds etc and anywhere that water tends to accumulate. This includes inside of doors, inside fenders, grille etc
6. I then use a drying towel to blot up any spots.
7. I apply a quick detailer post every wash. Its a ceramic coating detailer that is easy to apply and boosts protection from UV etc.
8. Proper wax/sealant is applied when I polish/detail the car (twice per year)
Products I use are usually from Chemical Guys range for shampoos, detailer, etc