Recognize your insecurities. What does that voice in the back of your mind say? What makes you uncomfortable or ashamed of yourself? This could be anything from acne, to regrets, friends at school or a past traumatic or negative experience. Whatever is making you feel unworthy, ashamed, or inferior, identify it, give it a name, and write it down. You can also tear these written pieces to start feeling positive on those points.
Talk about it with friends and loved ones. Wear it on your sleeve. Each day you should chip away at it; wear it down. There's no quick fix. Get to the root of the problem; focus on it and understand that you need to resolve each issue before you can move on. Check if it's an old past emotion and if it is really still relevant or applicable in your life today. And that doesn't mean you have to get rid of whatever makes you feel bad (many times, you simply can't). You need to learn to accept yourself, your past, your circumstances as they are, without necessarily thinking of them as "bad".
Bounce back from your mistakes. Remember that no one is perfect. Even the most confident people have insecurities. At some point in any of our lives, we may feel we lack something. That is reality. Learn that life is full of bumps down the road. And that often these insecure feelings come and go, depending on where we are, who we are with, the mood we're in, how we are feeling. In other words, they are not constant.
Identify your successes. Everyone is good at something, so discover the things at which you excel, then focus on your talents. Give yourself permission to take pride in them. Give yourself credit for your successes. Inferiority is a state of mind in which you've declared yourself a victim. Do not allow yourself to be victimized. Express yourself, whether it's through art, music, writing, etc. Find something you enjoy. Everyone is born with talents and strengths. You can develop and excel in yours. If it's difficult to name two or three things you have some ability in or just plain love to do, think about things others do that you would like to do too and take some lessons or join an enthusiasts club. When you're following your passion, not only will it have a therapeutic effect, but you'll feel unique and accomplished, all of which can help build your self confidence. Plus, adding a variety of interests to your life will not only make you more confident, but it will increase your chances of meeting compatible friends!
Be thankful for what you have. A lot of the times, at the root of insecurity and lack of confidence is a feeling of not having enough of something, whether it's emotional validation, good luck, money, etc. By acknowledging and appreciating what you do have, you can combat the feeling of being incomplete and unsatisfied. Finding that inner peace will do wonders for your confidence.
Be Positive, even if you don't feel the same way. Avoid self-pity, or the pity and sympathy of others. Never allow others to make you feel inferior--they can only do so if you let them. If you continue to loathe and belittle yourself, others are going to do and believe likewise. Instead, speak positively about yourself, about your future, and about your progress. Do not be afraid to project your strengths and qualities to others. By doing so, you reinforce those ideas in your mind and encourage your growth in a positive direction.
Accept compliments gracefully. Don't roll your eyes and say, "Yeah, right," or shrug it off. Take it to heart and respond positively ("Thank you" and a smile works well).
Look in the mirror and smile. Studies surrounding what's called the "facial feedback theory" suggest that the expressions on your face can actually encourage your brain to register certain emotions. So by looking in the mirror and smiling every day, you might feel happier with yourself and more confident in the long run.
Fake it. Along the same lines of smiling to make yourself feel happy, acting confident might actually make you believe it. Pretend you're a completely confident version of you; go through the motions and see how you feel!
Stick to your principles. It might be tough, but if you don't have something you can believe in, you don't have anything. If you don't stand for something, you will fall for anything. No matter what's happened in your life, you can always lay claim to the fact that from this day forward, you've followed your principles to the best of your ability.
Help others. When you know you're kind to the people around you, and are making a positive difference in other people's lives (even if it's just being kinder to the person who serves you coffee in the morning), you'll know that you are a positive force in the world--which will boost your self confidence.
Avoid perfectionism: Perfectionism paralyzes you and keeps you from accomplishing your goals.
