1. Proportions - hood length, width/height ratio, etc etc etc. They have to either be a.) in balance, or b.) deliberately outrageous, but in a way that “works” from all angles. This will obviously vary for different types of vehicles

2. Form over styling details. This is a huge mistake many modern designers make. They rely on brand cues - headlights, grilles, body cladding, huge badges, trim bits, etc. - to style a vehicle rather than focusing on the shape. Mazda and Volvo are examples of mainstream makes doing it right. Both make beautiful cars. The cars rely on their shapes, proportions, and a couple signature styling cues to look sexy. Lexus is a great example of what not to do - slather too many eye-catching brand details over a frumpy body (LC notably excluded).

3. An appearance of lightness and sleekness (for small cars or sports cars or cars) or solidity (for large cars or trucks/SUVs), rather than looking bloated, overweight etc. Think athletes/models vs. obesity. Too many cars look fat these days - bulbous hoods, swollen bodies, heavy-handed rooflines and pillars, too-tall rear ends. GM and Toyota’s mainstream vehicles are among the worst offenders. Mazda, Volvo, and VW are doing it right.

Ultimately though, a beautiful car is one that makes me stop, take an extra look, and say “Whoa”.

For me, sports cars are easiest to make beautiful because their styling is less constrained by practical needs. Most of the cars on my as-yet-unwritten “most beautiful” list are two-seaters or 2+2 GTs.