Do you ever notice when you're genuinely happy and you smile at your son he almost always smiles back with the same genuine fervor?
Do you notice when your attitude is very positive your daughter always responds back with the same positivity despite being in the midst of a tantrum?
It never fails.
It's like these kids (pre-3 yr old as far as I know) possess an innate bullshit detector that we all lose as we get older. Actually we don't lose it but it transforms into different type of BS detector --one that detects layers and layers of bullshit, I guess.
What does that tell you?
If you desire a specific positive behavior from a child (good temperment, good grades, etc) you must be true to them. And that means you can't pretend you've been doing positive things when you've really been out there with your homies snorting coke or screwing whores. A consistency between what you've actually been doing and what you want to present yourself as been doing needs to exist and needs to be legit.
Kids can see through your charlatan ass.
Keep it real, always.
Lead by example.