1. Put them always in the same place. Especially the "back" or "exit" button!

2. Each button should do one thing, not switch between 3 or more modes that you should look to understand which one you've just activated. Negative example: one button to cycle from cuise control, to drive assist, to speed limit, and back to off.

3. The area where a tap is interpreted as a button press should not also be where a swipe is recognized. In moving vehicles it is too easy for your finger to swing just an inch before touching the screen.

4. The active area of a virtual button must be large, larger than the icon it displays, so large that you shouldn't be distracted from driving just to aim at it!