Murakami taught me how to live alone: go food shopping and get a case of beer with your groceries. Don't eat things if you don't know where they came from or how they're made. Read a book once in a while.
Remember that sex isn't something you can use to judge yourself or judge other people. It rarely reflects on those involved, it just happens sometimes - like rain in Summer, or sunshine in Winter. Enjoy both. Never become too attached.
Cook nice things, even if you have to burn a thousand slices of toast and occasionally live off of instant noodles. Go outside once in a while.
Realise that exercise is necessary. This might mean jogging on the spot in your room because you can't breathe well enough to run, or doing sit-ups alone because gyms are expensive and frightening. Take care of your body. It's going to belong to an old person one day.
Never turn down friends to do something that can wait. You don't know how lucky you are until they stop calling.
If someone is sat on the side of the street in the cold, asking you for money, have the courtesy to apologise if you don't want to. Better yet, give them some change, without being condescending and worrying about how they're going to spend it. If you don't need something, find someone who does.
Realise that Store Cards are there to make money for that shop. Care about your appearance, but not so much that you find yourself in debt.
Meet new people, and be there for those you already know. Love one another.