Think about it: 
As annoying as your child’s lack of manners can be, resist the urge to reprimand him in front of other people. I’ve seen many parents do this. In a misguided effort to teach manners, they display some of the worse manners I’ve seen!
 
Teach them what to do:
Many children are not aware of their bad manners and must be taught not only what not to do, but what to do instead. For example, if a friend of yours speaks to your child, who looks down at his sneakers and ignores the comment, it’s typically embarrassment and ignorance on the child’s part that’s causing the behavior. After the person leaves, make a brief comment to your child, “Casey, if an adult talks to you, it’s polite to look him in the eye and say something back. When Mr. Nagamine commented on your new shoes, you could have said, ‘Thank you, they’re new.’  People like it when you answer them like that.”

Correct privately:
If your child is acting in a rude way, lead him away from other people and quietly and briefly correct him. Give him a smile and a hug to show him that you love him. That way you can send him back into the situation prepared to change for the better.

Have clear expectations:
In advance of a social situation, brief your child on what manners will be expected of him. Younger children can benefit from a role-play at home previewing what they might expect.

Give lots of praise:
Praise your child for using good manners. Believe it or not, children often feel embarrassed when they socialize with adults and use good manners. Since they have heard adults say things like, “Fine thank you, and you?” they feel like an impostor when they say it themselves!