1. QUALITY, NOT QUANTITY. It does not matter HOW MANY friends you have, it's about WHO your friends are. It's better to have a small group of friends who truly care about you than to have a lot of friends who could care less about you.
2. Don't be afraid to say no. For some odd reason, we believe that saying no means we will hurt someones feelings. That's not necessarily true. Saying no to going out, or to foods we can't eat, or to people we can't hangout with means this: "I am not trying to hurt you, but I need to take care of myself right now".
3. I am just as guilty of this, but frivolous spending can hurt you in the long-term. Save money, make financial goals, take care of your finances for moments where you might need them.
4. I am guilty of this too. In fact, I think everyone is. I am a futuristic person, but sometimes we need to enjoy the moment. We can plan for tomorrow all we want, but being in the moment is something we are only given once, and never again. Before we know it, time slips away. Be present with those around you.