Let me take a different tack. I'm 62, so not a "youngster" and I'll tell you my bad habits.
1. Mashing instead of spinning. I'm getting better but I still find myself riding like I have my old balloon tire bike from my youth.
2. Not drinking water before I get thirsty. I wait too long to drink water and then it can be hard to quench the thirst no matter how much I drink.
3. Moving up on somebody's right. That's a blind spot and bad manners.
4. Not signaling when I slow down. I forget my bike doesn't come with brake lights.
5. Not down shifting early on hills. Hard to shift when the chain has a lot of tension on it.
6. Always wanting to be in front. It's not a race and I don't have to prove anything.