Teaching my boys to look people in the eye and give a firm handshake
My 8 year old met my boss the other day and I could see him trying real hard to remember what I taught him. He looked up, shook his hand properly, and said nice to meet you sir. My boss said something to me later about how respectful he was. That's what it's all about. These things matter even when the world says they don't. You teach your boys to be men of their word and to respect their elders, and that carries them through life.
Respect. Teaching the handshake and eye contact early makes a real difference. My oldest is 10 now and people comment on his manners all the time because we drilled this stuff young.