Many people don't speak up or take action, because they lack confidence. So how does one gain confidence? Of course most people gain confidence over the course of life, but that's rather slow. Then there's the famous "fake it 'til you make it", and other such tricks, but even those are much easier said than done -- and tend to lead to bravado, not confidence.
What do I recommend instead? Go join Toastmasters International. Yes, most people think of it as a public speaking training organization, but those skills are only part of what you can get out of it. It will certainly help you learn those skills... and other forms of communication... and leadership... and help you conquer any fears you may have of those tasks.
Along the way, though, it will also help you be much more confident, not just in the course of giving a speech or being suddenly saddled with some sort of leadership responsibilities, but in general as well. I for one know that, had I never joined Toastmasters, I would never have dared to do -- in some cases, might not have thought to do -- many of the things that made me the success I am today... or even to start this blog.
Now it's your turn. How did you conquer the nagging fears holding you back, and gain the confidence to Dare to Excel?