You can read more books about public speaking, I like the books of Dale Carnegie:
The Art of Public Speaking
How to Win Friends and Influence People
How to Develop Self-Confidence And Influence People By Public Speaking
The Leader in You
To name a few...you can search it on the net for more books of Dale Carnegie, if you haven't already.
And also, Developing the Leader Within You by John Maxwell.
These books can help develop your inner confidence about yourself and develop meaningful relationship to others as well.
But in order to speak well, you must first LISTEN well from others, and equip yourself with enough knowledge about the topic or company, in order for you to speak appropriately specially during job interviews.
And lastly, just RELAX, we are all just humans after all. Trying to make sense of our lives.