I'm not here to patronize you.  We know if you walk with better posture, force a fake smile, or get a new haircut you can trick your brain and boost your self-confidence.  Perhaps for 20 minutes you'll think you're the next Richard Branson. 
I'm here to tell you there are proven ways to improve your self-confidence that will drive real, long lasting change in your life.

1. Meditate 

When we feel insecure, it manifests itself in myriad ways. Our bodies don't work. We can't focus. Insecurity creeps in when we're not living in the present moment.
Taking control of our monkey brain is a profound step toward true self-confidence.  I recommend you try the Headspace app.  You can select five minute, 10 minute, and 20 minute simple guided meditations. 

2. Think inside the box

Having the freedom to make choices with your time might be one of the main reasons you decided to become an entrepreneur.
But too many options can be your downfall.
We speak in platitudes that we think carry weight--like "think outside the box." There is a freeing joy in thinking inside the box. Executing on what you know, focusing, and moving the needle are empowering.

3. Learn something new every day

The average audio book is 10 hours. If you commute 60 minutes a day, you can listen to about 24 books a year.
That's a life changing habit. The more knowledge you have, the greater your confidence will be. Simple. Check out Audible for some choices.

4. Teach

If you're an expert in your field, sharing your knowledge will add to your fulfillment as a human being. Feeling fulfilled will add to your confidence.
If public speaking terrifies you, consider posting content on platforms like LinkedIn or Medium. Or you can create an online course on Teachable.com.

5. Take control of your career

The best way I know of to do this is to launch your own personal blog. I recommend the URL be: first name, last name DOT COM.
It's a simple notion. If you take control of your personal brand and create content that inspires you, confidence will follow. If you're ready to launch your blog, than you can start here. I created a 24-step tutorial that shows you how to do it in 15 minutes.

6. Exercise

Instead of buying expensive clothes, you can workout. Clothes will fit better. Instead of trying to walk with your shoulders back, exercise. Your core muscle strength will enhance your posture and gait.
Instead of buying skin products, exercise and hydrate. Your skin will look better. Instead of forcing that fake smile to make you feel happier--exercise. The Mayo Clinic says, "You may also feel better about your appearance and yourself when you exercise regularly, which can boost your confidence and improve your self-esteem."

7. Get more sleep

If you have trouble sleeping, try the Sleep Cycle app. Getting enough sleep helps your brain and body. The Harvard Mental Health Letter states: "The deepest stage of quiet sleep produces physiological changes that help boost immune system functioning."
Sleep Cycle helps you see when you fall into the deepest, most healing stages of sleep. It goes off with a gentle chime that wakes you at your peak awakeness cycle. Better sleep, sharper mind, better mood, and greater self-confidence.

8. Volunteer and give back

I used to volunteer at the Den for Grieving Kids in Greenwich, Connecticut.  September 11th happened. My fellow volunteers became my support network.
I thought I was giving. I thought I was sacrificing.  All the love I cold conjure couldn't match the love I felt from that group in the weeks and months after 9/11.  Who knows, you may heal someone, and you may heal your own soul.

9. Socialize

This can be a difficult one for introverts. Socializing, or finding your tribe, doesn't always have to happen in person. Joining an online community of like-minded people can enhance your self-worth.
Abraham Maslow's hierarchy of needs includes belongingness among the essentials. Contributing on Quora or posting compelling content to your network on LinkedIn can create a real sense of belonging. Similarly, building community via your Twitter account can also stimulate this powerful feeling.

10. Get curious

Seek people who are more experienced than you. Learning from them will instill a powerful calm of knowing. Chances are, the lessons they share will be invaluable.
Most "overnight success" stories have experienced the trials and tribulations that you may also be experiencing. They have all survived and may be able to help you.