Often, we are taught that self-confidence can be built by focusing on how we walk, talk, shake hands, and make eye contact. But these are only outward signs of confidence, and they can be faked. The answer to obtaining real self-confidence is to practice self-efficacy. Note that I said you will need to PRACTICE self-efficacy. Self-confidence is a state of BEING. Self-efficacy is a state of DOING. The only way to change what you ARE is to change what you DO.
What is self-efficacy? It is the certainty that you can accomplish any task or goal that is set before you, even though you may not know how to proceed. In other words, you are certain that, one way or another, efficient or sloppy, you can figure out the solution to any problem. The primary benefit of this thinking is that it puts you in a frame of mind to ask questions and gather knowledge so that you will be prepared and have a far greater chance of success. Confidence is the natural byproduct of self-efficacy.
How can you practice self-efficacy and build the confidence that follows from it?
1. Replace "can't" with "how". Never say, "I can't do it." Instead, say "how can I do it?" This will focus your mind on the solution rather than on the task. When Walt Disney wanted to make color cartoons his brother complained that the paint would probably chip off the celluloid. Walt responded that they would figure out how to develop paints that wouldn't chip off. He didn't have all the answers, but he knew that he could, one way or another, find a solution. And he did.
2. Realize that others have successfully done what you are trying to do. Except in rare cases, this is probably true. That means that the answer is out there, even if you don't know what it is. Ask the "how" to put yourself in a frame of mind to find the solution. Talk to someone who has accomplished the goal you are setting out to achieve. Knowledge and interaction with other successful people will build your confidence. Walt Disney didn't find the solution to his paint chipping problem, but he knew the people who could solve it.
3. Recall past successes, no matter how small. You have found solutions in the past, you can find them again for your current goals. Past successes reinforce and validate the fact that you should be confident in yourself.
4. Forget perfection. First and foremost, be effective. Efficiency will come later. The opening of Disneyland in Anaheim was a disaster. It was overcrowded, it was hot, there weren't enough drinks, the park wasn't completed, there was a gas leak, and people were miserable. Consider Disneyland today. Confidence is built when goals are achieved, regardless of how perfect or imperfect the results are.
So, forget about the traditional idea of self-confidence. Focus on practicing self-efficacy. Ask "how", seek the solution, remember your successes and just get it done. Self-confidence will be the byproduct.