To acquire confidence you need to spend some time analysing yourself and taking [a mental] note of what are your qualities and defects.
After you have sorted those out, you could work on calling the attention to your qualities. I don't mean bragging, I mean letting them show more often. Maybe try new ways to use those qualities in other departments in your life.
As you do that, you can gradually start working on your weakest points to improve what you feel needs improvement. As time goes by you'll feel more confident.
Confidence is a funny thing. It is the only thing where I trully believe that, before you see it, you must believe it.
If you keep repeating to yourself that you can achieve something, in time that will change your mindset and will help you work towards your goals.
So, ridiculous as it may sound, it IS indeed a good thing that you, for instance, stand in front of the mirror and say to yourself "you're awesome, you can be anything you set yourself out to be, you are THE MAN".
However, confidence doesn't only come from self complimenting. You need to take action. Otherwise you're just lying to yourself.
So, GO FOR IT!
