In a nutshell: No shortcuts.
Unfortunately, scratching your vehicle is possible whenever you touch it. A proper wash thus seeks to reduce the likelihood of scratching as much as possible. Washing safely is accomplished by combining the right gear with quality products and proper techniques.
A proper wash begins with a pressure washer. These machines use less water than hoses and clean better by removing more dirt from the paint’s surface. Pressure washers also have “foam cannon” attachments which coat your entire vehicle with soap. The combination of this automotive bubble-bath with a pressurized rinse means you can remove a significant amount of dirt from the car without even touching it.
Technique: rinse, cover the car with foam and allow the soap to dwell on the surface. After waiting for 3-5 minutes, rinse heavily soiled areas a second time. Proceed to Step 2.
3 buckets are necessary for a proper wash. One contains soapy water, another rinse water. The third is designated for use only on wheels. The soap and rinse buckets are self-explanatory. They keep your paint safe by separating clean, soapy water from dirty water. A third “wheel bucket” is necessary to keep jagged metallic particles in brake dust away from your paint. (note: this is less of a concern for cars with carbon ceramic brakes, although a third bucket may still be used)
Proper washing is also done with a wash-mitt/pad made from microfiber, wool, or some other synthetic material. These tools trap dirt in their tiny fibers, lifting the abrasives off the paint.
Technique: wash from top to bottom. Move your wash-mitt/pad across each panel in strait lines to reduce the chances of creating a circular scratch (easier to see and harder to remove than a straight scratch). Flip, rinse and reload the mitt/pad with soap as it becomes dirty. Rinse all the soap off the car once you have covered all surfaces.
Drying your car should be done with microfiber towels and a “drying-aid.” Many use microfiber, but few use a drying-aid. This extra product, whether a general detail spray or a polymer specifically made for drying, reduces scratching by adding lubrication between your towel and the paint. Using compressed air or a blower of some sort also helps to reduce drip marks and water spots by pushing water out of hard to reach places.
Technique: mist each body panel with your drying-aid of choice and dry in straight lines. Check, flip and replace towels if they become dirty from areas missed when washing.