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!