Watch your breath.
Breathe in through your nose and out through your mouth, following your breath as it travels. Let go of all stressful thoughts.
Observe your world.
Looking around you, find something that comes from nature, such as a plant and focus on it. Notice very aspect of it and contemplate all it does in connection to you and the outside world.
Every time you experience a negative thought, acknowledge that it is unproductive. Rather than letting it fester, dispel it from your mind.