First, keep learning. If you don't know, you will lack self-confidence. So first of all, keep studying about the subject you want to increase your self-confidence in.
Second, keep mixing with people who are more skilled and competent than you. Then your experience and work skills will increase and your self-confidence will increase. They will not want to give you time, you will have to take the opportunity and get closer to them, try to get their attention.
Third, improve your work. Develop quality. Increase your skills. Learn to work with a big plan. Try to do a job better today than you did yesterday. Try to talk smarter today than you did yesterday. Try to increase your network today than yesterday.
Take small risks if necessary. If you don't work without taking risks,
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