I have so much to say on this subject, though I really hate to ramble on. This year I have changed my self esteem dramatically. As a teenager I hated my life. I was a headcase who struggled with depression and anxiety disorders related to having no self esteem.
It took less than a month for me to reverse all that. I am now a confident optimist. I feel powerful everywhere I go, in everything I do.
I think the biggest realization I made was that humans are too goal oriented. We get so wrapped up in succeeding that we don't know how to handle failure and we forget to have fun either way.
There are things in life that give us a false sense of self worth. School, work, romance etc.. Say you ace an exam in school. You feel great about it, but if you fail the next one, you feel useless again. you would have relied on something external to make you feel good about yourselves. If we try a different approach though, and try to learn the subject material for the sake of learning, there is no pressure. Just ignore the outcome and focus on the path. Not only will you probably get a better grade, but you will also handle it better if you get a poor grade.
This can apply to almost any aspect of life. If you can force yourself to enjoy a boring every-day task, you will stop worrying about the outcome. This is a hard part at first. I just try to turn everything into a game. Pick a tile on the floor in front of the washing machine. Now do your laundry really fast without stepping on that tile! Silly but it works. The outcome does not matter, only that you enjoy yourself while doing it. Enjoy yourself and your self esteem will never be a problem.
I also notice that I can change my mood almost instantly by forcing myself to change my body language. Here's some random things that help:
Posture: Keep you back straight and your chin up. Take deep breaths drawing air into the bottom of your tummy. It takes practice to keep this going all the time, but it's worth it. Throughout the day, ask yourself how your posture and breathing are.
Smile. If you don't feel happy, then fake it until you do. I imagine a sort of "inner smile". Like a face inside my head just behind my actual face. Imagine it smiling and pulling you into a real smile with it. alternately look in the mirror and smile. I mean just the biggest most absurd smile you can manage. Think about how dumb you look by doing that and laugh about it. Did your smile just become a real one?
One last thing. And it's important.
If you have low self esteem, you probably think about what other people think of you...more than they actually think of you. Try to stop caring about what other people think of you. I know, easier said than done.