My personal experience with her started years ago when I started exploring the Hindu Pantheon. My interest was piqued when I learned that my home in the Philippines was once a seat of the Majapahit Empire. Since I first started chanting to Ganesh (Remover of Obstacles) and Lakshmi, my fortunes have definitely improved.
The practice of mantra is done with a Mala or Rosary consisting of 108 beads. I have learned to recite the mantras repeatedly until I put myself into a semi-trance.
Here are some mantras courtesy of Puja.net
For overall spiritual growth use the Lakshmi Gayatri Mantra:
OM Maha Deyvicha Vidmahay
Vishnu Patnicha Deemahee
Thanno Lakshmi Prachodayat
For financial benefit:
OM Shreem Maha Lakshmiyei Namaha
For greater happiness:
OM Shreem Shree-aee Namaha
For overall abundance:
OM Hreem Shreem Kleem
Maha Lakshmi Namaha