Well, I have a thirteen year old as well, and the best way to validate a young teenager is to give him or her non-judgmental positive regard. This is a way to boost self-esteem because when you give unconditional support coupled with a caring expression, it will lead to self-affirmation.
To teach a young teen to be more respectful with others, try role-playing! Do a role-play of a rude exchange, and then do a role-play of a polite exchange, and ask your teen to note that the polite communication is preferable. Explain to your young teen that it is easier to catch more bees with honey, and that her needs will always be better met with having polite exchanges and respect for others.