Start small.
If you want to achieve something big, you have to start small.
This can be applied to anything...
To follow on from ideas 1 and 2, if you want to own your success, or deliver genuine criticism that you believe will help someone - start small and start soft, and build your confidence from there.
If you want to start going to the gym, start by turning up and calling that a win. Spend 20 minutes at the gym twice a week, another win. 30 minutes 3 times per week, a win.
With every step you take you will get better, you will build confidence, and you will want to do it more.
This is how all great things start, by a series of small wins coming together - developing a lifestyle and engraining habits along the way.