Meditation is easy to incorporate into everyday life and can help eliminate negative thoughts. For example, try meditating for 10–15 minutes first thing each morning. This helps relax the mind and sets you up for a positive mental attitude to start the day. 
A recommended practice for managing stress, particularly in situations such as commuting on public transportation, is mindfulness meditation. Examples of mindfulness techniques include concentrating on the breath or engaging in a mental "body scan." Such meditation helps anchor oneself in the present moment, fostering a sense of calm and awareness.
Here’s an example of what this might sound like: “Focus your attention on your feet. It’s normal for distracting thoughts to appear, but as soon as you notice them, return your attention to your feet,” then gradually move your attention further up your body. There are also wonderful audio experiences that take you on mental journeys to a mountain lake or the sea. 
In addition to meditation, try options such as Jacobson’s progressive muscle relaxation technique or autogenic training.
Progressive muscle relaxation involves tensing and relaxing certain muscle groups in sequence. The benefit is that some techniques can be applied almost anywhere subsequently. 
Autogenic training is based on autosuggestion. It relies on a comfortable body position where the muscles can completely relax. You should then perform the exercises, which involve silently repeating short statements in your head. 
For instance, you can move down your body in your mind, right leg, left leg, then right arm, left arm, etc., imagining that your limbs are getting progressively heavier (as though you’re lifting them out of water).