What is the worst possible outcome from undertaking a particular course of action? List down all the scenarios on a piece of paper. Then write the likelihood of occurrence against each outcome (maybe, not really, or certain). Then proceed to write what you would do if a particular outcome actually occurs.
For instance if you are afraid to start a business you can list down all the bad things which might happen to you. You may go broke. Your may utterly fail. You may have to give up your job, etc. Going broke may probably happen. If this happens you could rely on your savings or move into a smaller apartment.
This exercise is a way to define and take control of your fears. Fear is most debilitating if it is not defined. Once you define it you can begin to take charge. If you go through this exercise you will realize that the things you are most afraid of are unlikely to happen. And if they do happen you can always do something about it.