In his writings and lectures Swami Vivekananda offered mantras or phrases to repeat.
Here are some:
Victory to Kâli! Victory to the Mother! Victory to Kali! Wâh Guru, Wah Guru ki Fateh (Victory unto the Guru)!
Om
Soham, Soham.
I am not the body, I am not the mind, I am not the thought, I am not even consciousness; I am the Atman.
Shivo’ham, Shivo’ham–I am Shiva! I am Shiva!
It is, It is
I am He!
I am Shiva, of the essence of Knowledge and Bliss!
Hara! Hara! Mahadeva!
Be it so! Be it so! I am Shiva! I am Shiva!
Yea, Yea, So’ham, So’ham–I am He! I am He!
I can do everything!
So’ham, So’ham, Shivo’ham
I am He! I am He! I am Shiva!