Shani Puja is done for Grah Shanti ,for mental peace and to get free from various diseases. Following things are associated with Shani.
Direction : West
Gemstone : Blue Sapphire (Neelam)
Metal : Lead
Ruling Day : Saturday
Flower : Vanni, Kuvalai
Color : Black
Associated No. : 7 (Seven)
Grain : Black Urad Daal
Food : Rice Mixed With Black Urad Daal
Dhyan Mantra :

“Nilanjana Samabhasam Ravi Putram Yamagrajam Chaya Mrttanda Sambhutam Tam Namami Shanai
Shwaram Shani Gayatri Mantra: Aum Sanaischaraya Vidmahe,Sooryaputraya Dheemahi, Tanno Manda Prachodayat.”

The planet Saturn is called Shanaishwara. Saturn is regarded as an emaciated God with long physique, big teeth and tawny eyes. Shani is indolent and lame. The temperament or nature of Shani is airy. It is believed that Shani can make a person, a king or a beggar according to the karmas.

“Aum Aing Hring Shring Shung Shanaishcharaye Namah: Aum”

One can do fasts on Saturdays and can take Khichri made of rice and black urad daal, after the sunset. Saturn gives all benefits to the devotees who pray sincerely to him.