One of the easiest ways to develop self-confidence and higher self-esteem is to become very good at something - perhaps your job.
Don’t be the guy who’s satisfied with mediocre work and says it’s “good enough”. If it’s only “good enough” it’s not.
Make a habit of doing everything you do as excellently as possible. Even if no one sees your work but you, imagine the CEO or president of the company is going to review your work. Before you turn in anything in writing, review it several times to catch any misspellings or grammatical errors, and always use Spell-Check. Imagine your English professor is going to review that report.
If your work hours are from 8:00 to 5:00, show up at 7:45 AM and don’t leave until 5:15 PM. It will be noticed.
Dress as professionally as is appropriate for your work place. If you work as a lawyer, CPA or stock broker, this probably means a well-tailored suit and tie. If you work in a tech industry, dressing professionally may mean a polo shirt, khakis and loafers. Dress like the CEO or president of the company dresses.
Make a habit of treating everyone you work with with respect and polite manners.
If you develop a reputation of being excellent at your work, as being highly professional in all your dealings with others and as being polite and respectful to everyone, you will earn the respect of others, and thereby become more self-confident and increase your self-esteem.