1. Admit your fears. In order for you to overcome your fears and take control of the situation you need to first recognise them. Admitting that there is a problem is the first step to overcoming any problem.
2. Understand that it's quite normal to get scared, or to be fearful for whatever reason, but that it's not normal to let your actions be dictated by these fears. You always have a choice (including the choice to take action), even if it seems like the more difficult thing to do at the time.
3. Consider what the lost opportunities would be if you decided to remain passive because of fear. Would you miss out on a bonus? A pay increase? A shot at a promotion?
4. Realistically look at your worst-case scenario. Is it really as bad as you think it is? And if it is, how long would it take you to recover if you were to fail?
In most cases simply recognising WHY you are fearful is half the battle. After you've pinpointed why you are afraid you can clear-headedly examine the possible scenarios and make a decision based on logic instead of fear.