If you want to reduce your negative thoughts, try the technique of compartmentalizing. Doing so will also help you reduce fear, anxiety, and tension.
Just as a train, submarine, and ship have different compartments, so can the mind. You can reduce your stress if you compartmentalize your negative thoughts. This may be easier for men who tend to think linear. But it can also be very helpful for women who tend to think in a more circular manner.
Think of your mind as having different compartments. When your thoughts bring feelings of anxiety, tension, or stress, place those thoughts in a compartment by itself. This compartment is watertight. Negative thoughts are sucked into this compartment. None other can enter.