I never really agree with "it doesnt matter what people think" philosophy. I mean a lot of people say they dont care what people think of them, but in actuality, they do. The way you can determine if you care what other people think of you is: Pretned you are on an island or the last person on earth. Act that way, dress that way. Because if you dont care what others think then that is exactly how one would act.

If you perceive yourself one way and 30 of your friends perceive you another way, which way do you think holds more weight. The reason most people are let down is because they just find out that someone thinks of them differently than they thought.

Say you think you are nice and polite and you think the girl you like thinks the same way about you. Suddenly you find out she thinks you are a jerk and rude. This is a let down because you are perceived differently than you think of yourself.

Basically, the first step towards self confidence is asking OTHERS how they perceive you. IE: Are you quiet, shy , aggressive, motivated, active, a leader, a follower, etc.
If you would like to more aggressive but are told you seem shy, ask that persons opinion of how he/she would perceive you to be aggressive. Ask your friends if you seem confident. Ask them what they feel your strong points are. Work harder on your strong points. If you excel in a certain area, it builds up your confidence.

Note: Family members will ALWAYS perceive you differently than friends and co workers. If you are the baby, you will always be thought of as the baby. Or always thought of as the older brother, etc.