The first step to take is to learn how not to dwell on the thoughts as they come to you. The more you reason, the stronger the thought becomes, it is just a fact. Try to focus your energy on an activity that is pleasing to you. The more you focus on recreational activities the easier it will be to forget it. Make it a priority to focus on something else the next time bad thoughts come into your mind. Believe it or not, you do have a choice of what you think about. You can cast down wrong thoughts. A good idea that I was told is to visualize a red stop sign in your mind when fear or fearful thoughts come upon you. Visualizing such a thing will help remind you that you should stop focusing on the thought and move on. It is important that you stop thinking of the negative and find something positive to replace it with. Next time you are bombarded with thoughts, take out your bible and focus on Gods word instead.
If you find yourself thinking many scary thoughts all at one time, you have to remember that getting upset will only make it worse. The thoughts you are having are not reality. Fear is a tactic of the enemy, nothing more. If you are able to be controlled by fear, the enemy has control of you. Your fears do not predict the future, no matter how much you believe you know what will happen in any given situation. So, it is best to just let it go and move on.
Although you may be saying that it is easier said than done, there are ways to overcome these thoughts. However, your focus must be on God and his strength, not your own. You can live a productive life; it is just a matter of changing how you think and what you spend your time focusing on. In fact, professionals have stated that it is the fear behind the thoughts that gives us the feelings we have, not the thoughts themselves. You must learn to ignore the fear behind your obsessive thoughts, no matter how the strong the fear may be to you. Eventually, if you ignore the fear that drives your thoughts you will starve them and they will go away.