To keep it simple, your main focus is to clean the car while inflicting as little micro scratches as possible. To that end the best way to do this is to do touch-free cleaning - things like snow foaming and pressure washing.
Products:
1. Pressure washer: Pretty much required to remove as much dirt without touching the car.
2. Snow Foam: Can be useful, again to apply soap to the car without the need to touch the panel. I would suggest applying the foam to a dry car instead of pressure washing first. Opinion does vary regarding this.
3. Wash with 2 buckets: One bucket of soap/water and one bucket of water. After wiping the car use the bucket of water to clear the dirt of the mitt so you aren't transferring the dirt back into your soap bucket.
4. Use a wash Mitt: Something that can absorb the dirt and move it away from the surface of it to reduce the chance of scratching.
5. Drying: Use a big plush microfiber towel, place on the panel and pat dry. Don't drag across the panel.
6. Decontamination products: You won't get everything off with just soap and a mitt, occasionally you should go over the car with fallout remover and tar remover. This builds up between the washes, you can do this every 3 - 6 months to keep on top of it.
Techniques:
1. Wash in straight lines, any scratches inflicted will be on a straight line and harder to see from certain angles.If you Mr Miyagi it and swirl, it'll catch the light no matter the angle.
2. Work from the top of the car down, usually the bulk of the dirt will be on the bottom and you don't want to drag this up the car.
For any damage that may already be present, good wash technique will obviously not cure this, your two options for this is to either cut the scratches back to smooth, or fill the scratches to temporarily mask the damage.
Cutting is done with a machine polisher and polish, I'd not recommend this unless you are comfortable with the concept.
Filling can be achieved with products like Autoglym Super Resin Polish (SRP)
