The Mantra has been taken by me from Brahma Vaivart Puran. - Ashok Mehta
The Mantra seems simple but many many gods and Rishis have gained Siddhi over this Mantra. The popular ones include Rishi Bhrigu, Shukracharya, Brihaspati, Valmiki and Surya.
Procedure of performing this Saraswati Mantra Sadhana:
1. Start this Mantra Sadhana from a Thursday or a Monday.
2. Sit facing the north direction in Padmasan on a White Aasan, wearing white colored clothes.
3. Keep a Chowki in front of you, spread a white cloth on the Chowki and keep the Yantra or Idol of Ganesh, Shiv, Surya, Vishnu, Lakshmi and Saraswati on the cloth. Light a Pure Ghee Diya in a copper or silver Diya. Earthen Diya are forbidden in Saraswati Upasana.
4. Do Guru Puja and then Puja of above mentioned 6 gods.
5. Recite the Saraswati Kavach.
6. Take a Sankalp for getting your desired wishes fulfilled.
7. Recite the Saraswati Mantra 4 lac times within 21 days using a White Chandan Mala or a Sphatik Mala.
Mantra: ।। श्रीं ह्रीं सरस्वत्यै स्वाहा ।।
This is a 8 lettered Mantra and can be chanted by anyone.
As I previously mentioned, the Mantra looks simple but many great gods and Rishis have done this particular Saraswati Mantra Sadhana.