When your mom was young, young ladies were expected to act a certain way. When your grandmother was young, the rules were even harder to follow. Today, things are a bit looser, but manners have not gone away completely. In fact, with new technology, there may even be more to learn to make sure you are being classy at all times.
I hope we all know the basics of good manners. When we ask for something, we say, "Please" to everyone. When we receive something, even if it's not our first choice, we say, "Thank you." If someone says thank you to you, you say, "You're welcome." Grunting, "Huh?" and "Hey you" are not polite. Instead, I'm sure you're already saying, "Yes" and "Excuse me" when you are called upon or need to get someone else's attention.
If you're already doing these things, or at least know you should be, you're about fifty percent there. Real manners take a lot more than a simple please and thank you, however even in the twenty-first century.
It doesn't matter how much money you have or how you dress. Everyone can and should be polite to others. It makes the world a nicer place, and it actually feels good too like giving yourself a nice pat on the back for a job well done. I said please and thank you aren't enough and here's why.
Teenagers are notorious for saying please with a sneer and thank you with an eye roll. If you roll your eyes and have a rude tone while mouthing polite words you are still rude. To be truly classy and polite, you have to go a step farther. You actually have to mean it or come as close as possible.
You don't have to sign your soul away to say thank you to the lunch lady at the cafeteria and nobody will make fun of you for inserting a pleasant "please" into, "Give me your roll if you're not going to eat it." Manners are a sign of respect, and we all like to be respected.
Class is in the Details
If you've accomplished the basics with meaning, you're ready for the serious stuff. A boy might try to open a door for you. Let him. It doesn't mean you're weak, it means he's got the kind of manners his father was raised with. And of course, say, "Thank you."
If you see someone struggling to open a door for any reason young kids, elderly, arms full of boxes, open it for them. If they don't say thank you, don't sweat it. Just think of how much more polite you are. You might even offer to help carry some of those boxes if you're heading in the same direction.
If a friend is telling a story, don't interrupt. It can be excruciating, but talking over someone else is rude.
Wait for her to finish and then share your thought. Speaking of interrupting, taking a phone call or responding to a text message is the same as blowing them off. At the very least, check to see who it is and say, "I'm sorry, I have to take this..." if it's someone like your parents. If it's just another friend, call them back in a little while. Finish with one friend before you start with another or you'll end up with no friends at all.
Entire books have been written about the finer points of manners such as crossing legs at the ankles and which fork to use when. If you don't feel confident that you are using the best manners, you can certainly find a book on the subject or just watch people around you. If someone is nice to you, it feels good. Return the favor by being nice to someone else. You will know you've done your share to make the world a nicer place to be.