2. Be interested in as much as you possibly can. People, subjects, activities...try to be curious and explore and inquire. No need to force yourself out of your comfort zone; I'm very risk-averse but can find loads of things to be interested in outside of extreme sports and adventure travel. (Well, I like hearing about extreme sports and adventure travel!) And I'm very much an introvert, but I discipline myself to keep up human connections. Keeping yourself connected to others and the world around you serves to keep you from shutting yourself in your own little world, where you could end up very lonely and longing for purpose.
3. Humanity is made up of Users and Usees...get to know the players. Usees are goodhearted, generous people who live by the Golden Rule, thinking of others' needs and not necessarily their own. Users are people who are, for whatever reason, mostly focused on their own happiness. And it seems like when in the presence of Usees, they can't help but take advantage. So it's important for nice people to develop the ability to not always take the Nice Road. Once you've pegged someone as a User, you have to watch out for your own interests--they are just as important as anyone else's.
5. Make smart decisions, with an eye to the "long view." Pay attention and take the good path at each fork in the road, asking yourself what the long term consequences will be. This really will make a difference in your life. One wrong choice that seems insignificant in the moment can drastically alter the rest of your life--just ask a pregnant teen, a drunk driver who hit someone, or a drug addict. I know it's common sense that smart choices lead to success...and yet we live in a world of people with maxed-out credit cards, don't we? Too many people can't think past today. Learn to do so, and your 20-years-older self will be a much, much happier person. You'll feel pretty good right now, too.
6. Put the kibosh on these behaviors: bitterness, self-loathing, envy, passive-aggressiveness. Some "negative" emotions can be constructive, I think. Grief is necessary and natural. Anger can be therapeutic and can be channeled into positive action. But bitterness only poisons the person harboring it. Self-loathing only cripples one's ability to improve. Envy is usually misplaced--the person you envy is probably as unhappy as you are, so you're wasting your energy. And passive-aggressiveness is a self-deluding game (see #1 above) that accomplishes nothing good.
Blog, I've done a decent job with most of these principles during my life, but I tell you, I can trace at least 75% of my unhappiness to the consequences of my neglecting them. 'Bout time I passed them on, I guess! Carry on, Blog, and good luck.