This is my answer on Quora for the question "How do you develop confidence when you have nothing to be confident about?" - I thought it would be interesting for others as well. Here you can find the link.
I will write what helped me, and I think it can easily be done by everybody who needs to build their confidence. I feel I have come a long way comparing to 4, even 2 years ago. My answer slightly differs from the others written so far and I hope it will be interesting for you to read (at least).
1) keep a running gratitude list
When my confidence and my performance goes down, it's the first thing I go to. What it does for me is that it helps me remember that I already have a lot of good things in my life already. And yes, I may even add a smile from a stranger and nice weather on the list as well.
2) keep a running list of small & big wins
She accepted to go on a date with me/I have finally managed to cook an exquisite omelet/steak/I got an empty place in a crowded bus/a salary raise, anything. It improves my mood instantly and makes me think of myself capable of moving mountains.
3) know what worked and what didn't (and act on it)
This goes hand in hand with the idea of integrity being your main generator of confidence - when you know that you do your best you are more confident.
I usually do this when I feel I have come to certain times when I feel I'm at crossroads or in a (big or little) stump. It gives me a sense of evolving, growing, becoming better with time and that helps a lot with the confidence part.
Put in order your finances, your career and other areas of life that are important for you. You can add here a thorough analysis of your dressing style, find on the internet and try on, make photos of what works for you and what doesn't, in order to know that you did your best to look good (you stated in the question details about being shorter than you wished - google "how to look taller for men", for example).
4) immerse in something that makes me loose track of time
Hobbies, going out with friends etc. I think that doing things that give you joy from time to time is a necessary luxury. I think about it as more of a pill that I need to take regularly in order to be able to function properly. For me, that's small DIY projects.
5) surround myself with people who believe in me or inspire me
Whether it's in person, as with coworkers/boss/friends, by telephone - for long-distance loved ones, or by watching interviews and reading biographies/blogs, I believe that the human factor makes it all worthy. I know that I feel very confident after a friend tells me (s)he is proud of me or pays me a compliment and after a pleasant discussion about future plans that seem very attainable after you share them with someone who believes in you. Or seeing other people do it.
That's what works for me. Building confidence is like healthy eating - you can make unhealthy choices sometimes, but you have to be committed to it and do every day what it needs to be done in order to keep the confidence momentum going. Good luck!