The Pradosh Vrat falls twice in a Hindu Lunar Month and commences at the time of Sunset on Trayodashi or 13th Tithi of both the Shukla Paksha [Bright Fortnight] and Krishna Paksha [Dark Fortnight]. However, there is no set manner or method of observing the Pradosh Vrat and the practice and rituals are likely to vary depending upon the localized preferences, customs and traditions. The practitioner can observe the Pradosh Vrat and perform the rituals, which he or she normally performs on this day, after, which the Mantra Prayoga described in this post can be practiced.
The Padmavati Mantra for success given below should be chanted 1000 times using any kind of Counting Rosary. After the completion of the required number of Mantra Chants, the practitioner should perform a Fire Havan and offer 108 Ashwagandha Flowers to the Agni; each time the practitioner offers the flower he has to chant the Padmavati Mantra.
ॐ नमो पद्मावती पद्मनेत्र वज्र वज्रांकुश प्रत्यक्षं भवति ||
Om Namo Padmavati Padamanetra Vajra Vajramkush Pratyaksham Bhavati||
The Mantra Sadhana should be performed for seven consecutive Pradosh Vrat. Another similar Mantra Sadhana for wealth and Money using the same Padmavati Mantra, which does not need the use of a Havan, can be seen here- Padmavati Mantra for Wealth.