Balancing safety habits with not becoming afraid of normal city life

Travel advice sometimes makes ordinary cities sound like obstacle courses: never look at your phone, never speak to strangers, never go out after dark. I take basic precautions and avoid wandering into unfamiliar areas when exhausted, but I also travel alone because I enjoy exploring. How do you keep useful safety habits from becoming constant suspicion? I'd particularly like practical routines that become automatic and leave you free to enjoy the rest of the day.