Another good place to practice concentration and focus, if you have the opportunity, is the subway. Especially in the summer, when it is blazing hot and crowded.
You can pay attention to everything that pulls you out of the present moment. A glance from a stranger. The heat. The noise. A body pressed against yours that you did not invite. The train sitting still in the tunnel for no reason anyone will explain.
None of it needs to be fixed. It only needs to be noticed. That is the whole exercise. You are not trying to make the car quieter or the ride shorter. You are watching how fast the mind runs off toward comfort, how it feels to bring it back, and how it runs off again a second later.
The subway is honest that way. It will not cooperate with you, and that is what makes it a better teacher than a quiet room.