Most people are careful during the wash and then rush the dry, wiping fast with whatever towel is nearest to get it done before water spots form. That's backwards. Drying drags a cloth across every panel with real pressure behind it, which makes it one of the most likely stages to put swirls into paint if the towel or the technique is wrong.
Why GSM matters
GSM (grams per square metre) is a measure of how dense a microfibre towel's pile is. A thin, low-GSM towel has less give, so grit sitting on the paint gets dragged rather than lifted. A properly heavy towel, 1200GSM is what I use and sell, has a deep enough pile that any dust or grit sinks into the fibres instead of scraping across the surface, and it holds enough water to dry a full car with one towel rather than needing three or four passes.
Step 1: Blot, don't drag
Lay the towel flat on the panel and press down, then lift, rather than wiping it across in long strokes. Dragging is what turns any trapped grit into a scratch. Blotting soaks up the water with far less friction.
Step 2: Work top to bottom
Start with the roof and windows, then bonnet and boot, then the sides, and save the lower panels and sills for last. The lower half of the car carries the most road grime, so drying it first just spreads that grit up onto the cleaner panels above.
Step 3: Change or rinse the towel halfway
A towel that's already picked up grit from the lower panels shouldn't go back onto the roof or bonnet. On a full valet I'll rinse the towel out or switch to a second one at the halfway point, rather than using one towel start to finish.
Step 4: Finish the shuts and mirrors last
Door shuts, fuel caps and mirror backs hold water that runs back out onto the panel if you dry them too early. Leave these for the very end so nothing drips onto a panel you've already finished.
Washing your drying towel
Wash microfibre towels on their own, never with regular laundry, fibres from towels, socks or anything else will embed in the pile and turn your "clean" towel into something that scratches on the next dry. No fabric softener either, as it coats the fibres and kills their absorbency.
Get the towel and the technique right and drying stops being the risky last step, it's just the last five minutes of a wash done properly.