1. Overt displays of self-interest/self-adoration. Avoid these. They are the social plague. If you are having trouble with this remember: You are the most important person in your life. Nobody else's. They've all got themselves to worry about. So shut up.
2. Don't bore other people. Simple in essence yet seemingly difficult in practice. There are warning signs to watch for that will let you know when you're company are falling into a boredom coma. If you find yourself repeatedly asking your company if you are being boring then 99% of the time you are.
3. Wash. No one wants to be asphyxiated by your mere presence. It's not a pleasant way to die.
4. Remember people's names. Again, sounds simple but difficult to implement. Try repeating people's names a couple of times during conversation when you first meet them. I'm terrible at this and it's a wonder that I've not been outcast already.
5. Don't complain. Negativity repels the optimistic, happy people that most of us generally aim to be chummy with. It also attracts other no-hopers to you who want to leech of your bad vibes. Before you know it you've been sucked in to a clique of miserable mopers watching the grass grow greener on the optimists' side. These groups are very difficult to escape.
6. Be brave. Don't be afraid to show your true colours to your friends and dance in the supermarket. Or anywhere else. They'll feel empowered by your freedom and love you for it.
7. Don't get stuck in a rut. We often get to the point in our lives where everything is compartmentalised, even people. We'll have a 'coffee friend' or a 'drinking buddy' and never will we push the boundaries of that relationship. Every so often, suggest that you do something different; go feed ducks at a lake, take a drive to your favourite look out or visit all the stores in your town that sell candy trying out all the tester plates. Shake it up.
8. Be nice. The most over-cliched and the most important step of all. Offer to help with no need of a return favour. Genuinely listen to other people and respond with enthusiasm. When someone you know does/says/wears something fantastic don't just notice it; tell them. And try to suspend your judgement of others for at least five minutes when you first meet them; give people a chance to impress you.
I am by no means perfect at any of these points. In fact, I can be remarkably terrible at all of them. We all can be. But you can only score points by trying. We all want friends, right?