Self-assurance/confidence can be a double edged sword. To much and you come off like a prick, but you can learn to channel it. Confidence is important, but makes it truely important is when you have confidence is what ever it is you do. You have to be confident enough in yourself that when you are going to be sincere with someone, say like them telling you something personal or important. You are confident enough that you can hear them out and make them feel secure in you. You have to have confidence in yourself when you begin to let someone into your life, its a hell of a thing to say to yourself that you trust someone enough to let them inside.
Also its important in how your confidence comes off. If you are overly showy, loud, and always condisending, you will drive people away from you. The best way to display confidence is in what you do, not what you say. Giving people a chance when you first meet them is important, many people fear strangers. But if you can deal with them and make friends, that says something about you. If you are able to be not just funny but serious when you need to be, that again says something. If someone slights you, its okay to say something back, but if you go out of your way to slight someone needlessly....
Let people see you in good spirits, the true mark of a confident man. Those who are easily shook and wear their fear on their sleeves often look like sheep missing from the flock. Temper your actions and words with fairness, kindness and understanding when they are needed and you will see people begin to look to you, especially the women. Just don't act like a doormat when someone tries to wipe their feet on you and you will do alright.
-Grey Fox