I was maybe 11 years old, the first time I tried to hop a curb. I think this has happened to every kid. The front wheel fell out of the fork. Loose nuts. This prompted me to do bicycle maintenance for the next 56 years. Also convinced me not to jump high curbs. My sidewalk riding is limited, but where I live, almost every curb is wheel chair accesssible these days.
Traits I wish every bike rider had? Mostly good manners. I hate it when two bikers ride abreast on a narrow path, taking up 60% of the width, and they see oncoming traffic and refuse to yield. What happens when two groups like this meet?
A skill I deem useful is shifting knowledge. If we ride our bikes like they had no motors, we would move up thru the gears while starting and downshifting back when stopping, keeping the gears in the best spot for easy pedalling and best use of our limited energy. With a motor, it's no different, but seems like people just wanna pipe in 1000 watts and twist a throttle.