1. Always say "Please" and "Thank You"
When asking for something, borrowing something, talking to someone about something, or any situation that may require you to say please or thank you, say it. This is a common manner that many forget, but it should be second nature. Please don't punch me in the face. Thank you for not punching me in the face. Common sense.
2. Always ask
This is a social skill that I am so happy my parents instilled in me, as it makes for less conflict and disruption between myself and other people. Do not take other individuals food, belongings, girlfriends, boyfriends, or anything else without asking. It is not polite to walk into someone's house you barely know and steal their things. Ask first. If you don't know them at all and they just happened to leave their door open or leave their things out I highly recommend just walking away and not saying anything. Do. Not. Steal. In all seriousness, always ask before you take a drink, a snack, or borrow a plate, utensil, or anything at all. Also, if you are at a party and you don't know the host, ask how you can help set up or prepare. They may say no, but at least you offered.
3. Hold the door for a lady
Really just hold the door for anyone. They may not say thank you, but that's not the point. Unless you know someone has a history of really enjoying the opening and closing of doors and it provides them with happiness, open it for them. It only takes a few seconds of your time and the right person may really appreciate it.
4. Leave an area as you find it
When it comes to entering any public place, a friends house, or a significant others house, it is your responsibility to leave the area as you found it. This means cleaning up your own mess, not relying on others to clean it for you. Wipe down messes you made, pick up belongings, leave things clean.
5. Chew like you have a secret
This one isn't really old school, but it does come from one of my favorite movies, "She's The Man." Do not chew with your mouth open in public. Do not talk with food in your mouth. Do not slurp like your drink is your oxygen. Do not lay your whole body across the table. Do not use forks to twirl your hair unless it is red and oddly doesn't get wet in water. Follow table manners. All of them.