Marinate Yourself In A Topic

Whenever you get a new assignment immerse yourself into it fully. Study everything you can find related to that subject. Attempt to become one of the most knowledgeable persons in that particular field. Figure out who is who and get the help you need to attain the expert level you aspire to. When I prepare a speech, for example, I think about oversampling, getting more data points, examples or stories than I will ever have time to use. In a similar way you can build your confidence and know you could handle any situation because you prepared yourself.