1. Not modelling good behavior for your children - expecting them to do what you say, not what you do. Kids sense the hypocracy and lose respect.
2. Not teaching critical thinking skills.
3. Being too germophobic. See "hygiene hypothesis".
4. Raising your kids just like you were raised because it "worked", or conversely, doing everything the opposite because it didn't. Take the good and reject the bad.
5. Parents fighting too many of the kid's battles for them, like arguing with teachers over grades, doing the kids homework or school projects for them, navigating the child's social relationships etc... It is tough, but there is a fine line between helping a child and taking over.