Live in the present. Imagining negative events infects your feelings and moods.
Our brain does not distinguish between real and imagined events. It uses the same mechanism to manage both real as well as imagined events. Thus, they have similar effect on our mind and body. If this seems difficult to believe, try this exercise. Think of a very close friend who you have not met recently. Close your eyes and imagine meeting your friend. Both of you are spending time together and doing what you like best in each other's company. Imagine this scenario, in full details, for a few minutes. Most of you would experience similar feelings as you are likely to feel in actually meeting that friend. Similarly, if you imagine something unpleasant, it generates associated negative feeling.
Whenever you are doing something, your brain is busy imagining all kind of outcomes. Imagining negative outcomes is likely to generate fear of failure. On the other hand imagining positive outcomes is likely to make you overlook actual risks. The best strategy is to focus your mind and efforts on the work that you are doing, without imagining outcomes.
Imagining positive outcomes occasionally is okay, since it motivates you. However, imagining negative outcomes should be avoided at all costs.